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linux/kernel/workqueue.c
Thomas Tuttle fa2563e41c workqueue: lock cwq access in drain_workqueue 
Take cwq->gcwq->lock to avoid racing between drain_workqueue checking to
make sure the workqueues are empty and cwq_dec_nr_in_flight decrementing
and then incrementing nr_active when it activates a delayed work.

We discovered this when a corner case in one of our drivers resulted in
us trying to destroy a workqueue in which the remaining work would
always requeue itself again in the same workqueue.  We would hit this
race condition and trip the BUG_ON on workqueue.c:3080.

Signed-off-by: Thomas Tuttle <ttuttle@chromium.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-09-14 18:09:38 -07:00

3829 lines
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/*
* kernel/workqueue.c - generic async execution with shared worker pool
*
* Copyright (C) 2002 Ingo Molnar
*
* Derived from the taskqueue/keventd code by:
* David Woodhouse <dwmw2@infradead.org>
* Andrew Morton
* Kai Petzke <wpp@marie.physik.tu-berlin.de>
* Theodore Ts'o <tytso@mit.edu>
*
* Made to use alloc_percpu by Christoph Lameter.
*
* Copyright (C) 2010 SUSE Linux Products GmbH
* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
*
* This is the generic async execution mechanism. Work items as are
* executed in process context. The worker pool is shared and
* automatically managed. There is one worker pool for each CPU and
* one extra for works which are better served by workers which are
* not bound to any specific CPU.
*
* Please read Documentation/workqueue.txt for details.
*/
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/signal.h>
#include <linux/completion.h>
#include <linux/workqueue.h>
#include <linux/slab.h>
#include <linux/cpu.h>
#include <linux/notifier.h>
#include <linux/kthread.h>
#include <linux/hardirq.h>
#include <linux/mempolicy.h>
#include <linux/freezer.h>
#include <linux/kallsyms.h>
#include <linux/debug_locks.h>
#include <linux/lockdep.h>
#include <linux/idr.h>
#include "workqueue_sched.h"
enum {
/* global_cwq flags */
GCWQ_MANAGE_WORKERS = 1 << 0, /* need to manage workers */
GCWQ_MANAGING_WORKERS = 1 << 1, /* managing workers */
GCWQ_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
GCWQ_FREEZING = 1 << 3, /* freeze in progress */
GCWQ_HIGHPRI_PENDING = 1 << 4, /* highpri works on queue */
/* worker flags */
WORKER_STARTED = 1 << 0, /* started */
WORKER_DIE = 1 << 1, /* die die die */
WORKER_IDLE = 1 << 2, /* is idle */
WORKER_PREP = 1 << 3, /* preparing to run works */
WORKER_ROGUE = 1 << 4, /* not bound to any cpu */
WORKER_REBIND = 1 << 5, /* mom is home, come back */
WORKER_CPU_INTENSIVE = 1 << 6, /* cpu intensive */
WORKER_UNBOUND = 1 << 7, /* worker is unbound */
WORKER_NOT_RUNNING = WORKER_PREP | WORKER_ROGUE | WORKER_REBIND |
WORKER_CPU_INTENSIVE | WORKER_UNBOUND,
/* gcwq->trustee_state */
TRUSTEE_START = 0, /* start */
TRUSTEE_IN_CHARGE = 1, /* trustee in charge of gcwq */
TRUSTEE_BUTCHER = 2, /* butcher workers */
TRUSTEE_RELEASE = 3, /* release workers */
TRUSTEE_DONE = 4, /* trustee is done */
BUSY_WORKER_HASH_ORDER = 6, /* 64 pointers */
BUSY_WORKER_HASH_SIZE = 1 << BUSY_WORKER_HASH_ORDER,
BUSY_WORKER_HASH_MASK = BUSY_WORKER_HASH_SIZE - 1,
MAX_IDLE_WORKERS_RATIO = 4, /* 1/4 of busy can be idle */
IDLE_WORKER_TIMEOUT = 300 * HZ, /* keep idle ones for 5 mins */
MAYDAY_INITIAL_TIMEOUT = HZ / 100 >= 2 ? HZ / 100 : 2,
/* call for help after 10ms
(min two ticks) */
MAYDAY_INTERVAL = HZ / 10, /* and then every 100ms */
CREATE_COOLDOWN = HZ, /* time to breath after fail */
TRUSTEE_COOLDOWN = HZ / 10, /* for trustee draining */
/*
* Rescue workers are used only on emergencies and shared by
* all cpus. Give -20.
*/
RESCUER_NICE_LEVEL = -20,
};
/*
* Structure fields follow one of the following exclusion rules.
*
* I: Modifiable by initialization/destruction paths and read-only for
* everyone else.
*
* P: Preemption protected. Disabling preemption is enough and should
* only be modified and accessed from the local cpu.
*
* L: gcwq->lock protected. Access with gcwq->lock held.
*
* X: During normal operation, modification requires gcwq->lock and
* should be done only from local cpu. Either disabling preemption
* on local cpu or grabbing gcwq->lock is enough for read access.
* If GCWQ_DISASSOCIATED is set, it's identical to L.
*
* F: wq->flush_mutex protected.
*
* W: workqueue_lock protected.
*/
struct global_cwq;
/*
* The poor guys doing the actual heavy lifting. All on-duty workers
* are either serving the manager role, on idle list or on busy hash.
*/
struct worker {
/* on idle list while idle, on busy hash table while busy */
union {
struct list_head entry; /* L: while idle */
struct hlist_node hentry; /* L: while busy */
};
struct work_struct *current_work; /* L: work being processed */
struct cpu_workqueue_struct *current_cwq; /* L: current_work's cwq */
struct list_head scheduled; /* L: scheduled works */
struct task_struct *task; /* I: worker task */
struct global_cwq *gcwq; /* I: the associated gcwq */
/* 64 bytes boundary on 64bit, 32 on 32bit */
unsigned long last_active; /* L: last active timestamp */
unsigned int flags; /* X: flags */
int id; /* I: worker id */
struct work_struct rebind_work; /* L: rebind worker to cpu */
};
/*
* Global per-cpu workqueue. There's one and only one for each cpu
* and all works are queued and processed here regardless of their
* target workqueues.
*/
struct global_cwq {
spinlock_t lock; /* the gcwq lock */
struct list_head worklist; /* L: list of pending works */
unsigned int cpu; /* I: the associated cpu */
unsigned int flags; /* L: GCWQ_* flags */
int nr_workers; /* L: total number of workers */
int nr_idle; /* L: currently idle ones */
/* workers are chained either in the idle_list or busy_hash */
struct list_head idle_list; /* X: list of idle workers */
struct hlist_head busy_hash[BUSY_WORKER_HASH_SIZE];
/* L: hash of busy workers */
struct timer_list idle_timer; /* L: worker idle timeout */
struct timer_list mayday_timer; /* L: SOS timer for dworkers */
struct ida worker_ida; /* L: for worker IDs */
struct task_struct *trustee; /* L: for gcwq shutdown */
unsigned int trustee_state; /* L: trustee state */
wait_queue_head_t trustee_wait; /* trustee wait */
struct worker *first_idle; /* L: first idle worker */
} ____cacheline_aligned_in_smp;
/*
* The per-CPU workqueue. The lower WORK_STRUCT_FLAG_BITS of
* work_struct->data are used for flags and thus cwqs need to be
* aligned at two's power of the number of flag bits.
*/
struct cpu_workqueue_struct {
struct global_cwq *gcwq; /* I: the associated gcwq */
struct workqueue_struct *wq; /* I: the owning workqueue */
int work_color; /* L: current color */
int flush_color; /* L: flushing color */
int nr_in_flight[WORK_NR_COLORS];
/* L: nr of in_flight works */
int nr_active; /* L: nr of active works */
int max_active; /* L: max active works */
struct list_head delayed_works; /* L: delayed works */
};
/*
* Structure used to wait for workqueue flush.
*/
struct wq_flusher {
struct list_head list; /* F: list of flushers */
int flush_color; /* F: flush color waiting for */
struct completion done; /* flush completion */
};
/*
* All cpumasks are assumed to be always set on UP and thus can't be
* used to determine whether there's something to be done.
*/
#ifdef CONFIG_SMP
typedef cpumask_var_t mayday_mask_t;
#define mayday_test_and_set_cpu(cpu, mask) \
cpumask_test_and_set_cpu((cpu), (mask))
#define mayday_clear_cpu(cpu, mask) cpumask_clear_cpu((cpu), (mask))
#define for_each_mayday_cpu(cpu, mask) for_each_cpu((cpu), (mask))
#define alloc_mayday_mask(maskp, gfp) zalloc_cpumask_var((maskp), (gfp))
#define free_mayday_mask(mask) free_cpumask_var((mask))
#else
typedef unsigned long mayday_mask_t;
#define mayday_test_and_set_cpu(cpu, mask) test_and_set_bit(0, &(mask))
#define mayday_clear_cpu(cpu, mask) clear_bit(0, &(mask))
#define for_each_mayday_cpu(cpu, mask) if ((cpu) = 0, (mask))
#define alloc_mayday_mask(maskp, gfp) true
#define free_mayday_mask(mask) do { } while (0)
#endif
/*
* The externally visible workqueue abstraction is an array of
* per-CPU workqueues:
*/
struct workqueue_struct {
unsigned int flags; /* W: WQ_* flags */
union {
struct cpu_workqueue_struct __percpu *pcpu;
struct cpu_workqueue_struct *single;
unsigned long v;
} cpu_wq; /* I: cwq's */
struct list_head list; /* W: list of all workqueues */
struct mutex flush_mutex; /* protects wq flushing */
int work_color; /* F: current work color */
int flush_color; /* F: current flush color */
atomic_t nr_cwqs_to_flush; /* flush in progress */
struct wq_flusher *first_flusher; /* F: first flusher */
struct list_head flusher_queue; /* F: flush waiters */
struct list_head flusher_overflow; /* F: flush overflow list */
mayday_mask_t mayday_mask; /* cpus requesting rescue */
struct worker *rescuer; /* I: rescue worker */
int nr_drainers; /* W: drain in progress */
int saved_max_active; /* W: saved cwq max_active */
const char *name; /* I: workqueue name */
#ifdef CONFIG_LOCKDEP
struct lockdep_map lockdep_map;
#endif
};
struct workqueue_struct *system_wq __read_mostly;
struct workqueue_struct *system_long_wq __read_mostly;
struct workqueue_struct *system_nrt_wq __read_mostly;
struct workqueue_struct *system_unbound_wq __read_mostly;
struct workqueue_struct *system_freezable_wq __read_mostly;
EXPORT_SYMBOL_GPL(system_wq);
EXPORT_SYMBOL_GPL(system_long_wq);
EXPORT_SYMBOL_GPL(system_nrt_wq);
EXPORT_SYMBOL_GPL(system_unbound_wq);
EXPORT_SYMBOL_GPL(system_freezable_wq);
#define CREATE_TRACE_POINTS
#include <trace/events/workqueue.h>
#define for_each_busy_worker(worker, i, pos, gcwq) \
for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++) \
hlist_for_each_entry(worker, pos, &gcwq->busy_hash[i], hentry)
static inline int __next_gcwq_cpu(int cpu, const struct cpumask *mask,
unsigned int sw)
{
if (cpu < nr_cpu_ids) {
if (sw & 1) {
cpu = cpumask_next(cpu, mask);
if (cpu < nr_cpu_ids)
return cpu;
}
if (sw & 2)
return WORK_CPU_UNBOUND;
}
return WORK_CPU_NONE;
}
static inline int __next_wq_cpu(int cpu, const struct cpumask *mask,
struct workqueue_struct *wq)
{
return __next_gcwq_cpu(cpu, mask, !(wq->flags & WQ_UNBOUND) ? 1 : 2);
}
/*
* CPU iterators
*
* An extra gcwq is defined for an invalid cpu number
* (WORK_CPU_UNBOUND) to host workqueues which are not bound to any
* specific CPU. The following iterators are similar to
* for_each_*_cpu() iterators but also considers the unbound gcwq.
*
* for_each_gcwq_cpu() : possible CPUs + WORK_CPU_UNBOUND
* for_each_online_gcwq_cpu() : online CPUs + WORK_CPU_UNBOUND
* for_each_cwq_cpu() : possible CPUs for bound workqueues,
* WORK_CPU_UNBOUND for unbound workqueues
*/
#define for_each_gcwq_cpu(cpu) \
for ((cpu) = __next_gcwq_cpu(-1, cpu_possible_mask, 3); \
(cpu) < WORK_CPU_NONE; \
(cpu) = __next_gcwq_cpu((cpu), cpu_possible_mask, 3))
#define for_each_online_gcwq_cpu(cpu) \
for ((cpu) = __next_gcwq_cpu(-1, cpu_online_mask, 3); \
(cpu) < WORK_CPU_NONE; \
(cpu) = __next_gcwq_cpu((cpu), cpu_online_mask, 3))
#define for_each_cwq_cpu(cpu, wq) \
for ((cpu) = __next_wq_cpu(-1, cpu_possible_mask, (wq)); \
(cpu) < WORK_CPU_NONE; \
(cpu) = __next_wq_cpu((cpu), cpu_possible_mask, (wq)))
#ifdef CONFIG_DEBUG_OBJECTS_WORK
static struct debug_obj_descr work_debug_descr;
static void *work_debug_hint(void *addr)
{
return ((struct work_struct *) addr)->func;
}
/*
* fixup_init is called when:
* - an active object is initialized
*/
static int work_fixup_init(void *addr, enum debug_obj_state state)
{
struct work_struct *work = addr;
switch (state) {
case ODEBUG_STATE_ACTIVE:
cancel_work_sync(work);
debug_object_init(work, &work_debug_descr);
return 1;
default:
return 0;
}
}
/*
* fixup_activate is called when:
* - an active object is activated
* - an unknown object is activated (might be a statically initialized object)
*/
static int work_fixup_activate(void *addr, enum debug_obj_state state)
{
struct work_struct *work = addr;
switch (state) {
case ODEBUG_STATE_NOTAVAILABLE:
/*
* This is not really a fixup. The work struct was
* statically initialized. We just make sure that it
* is tracked in the object tracker.
*/
if (test_bit(WORK_STRUCT_STATIC_BIT, work_data_bits(work))) {
debug_object_init(work, &work_debug_descr);
debug_object_activate(work, &work_debug_descr);
return 0;
}
WARN_ON_ONCE(1);
return 0;
case ODEBUG_STATE_ACTIVE:
WARN_ON(1);
default:
return 0;
}
}
/*
* fixup_free is called when:
* - an active object is freed
*/
static int work_fixup_free(void *addr, enum debug_obj_state state)
{
struct work_struct *work = addr;
switch (state) {
case ODEBUG_STATE_ACTIVE:
cancel_work_sync(work);
debug_object_free(work, &work_debug_descr);
return 1;
default:
return 0;
}
}
static struct debug_obj_descr work_debug_descr = {
.name = "work_struct",
.debug_hint = work_debug_hint,
.fixup_init = work_fixup_init,
.fixup_activate = work_fixup_activate,
.fixup_free = work_fixup_free,
};
static inline void debug_work_activate(struct work_struct *work)
{
debug_object_activate(work, &work_debug_descr);
}
static inline void debug_work_deactivate(struct work_struct *work)
{
debug_object_deactivate(work, &work_debug_descr);
}
void __init_work(struct work_struct *work, int onstack)
{
if (onstack)
debug_object_init_on_stack(work, &work_debug_descr);
else
debug_object_init(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(__init_work);
void destroy_work_on_stack(struct work_struct *work)
{
debug_object_free(work, &work_debug_descr);
}
EXPORT_SYMBOL_GPL(destroy_work_on_stack);
#else
static inline void debug_work_activate(struct work_struct *work) { }
static inline void debug_work_deactivate(struct work_struct *work) { }
#endif
/* Serializes the accesses to the list of workqueues. */
static DEFINE_SPINLOCK(workqueue_lock);
static LIST_HEAD(workqueues);
static bool workqueue_freezing; /* W: have wqs started freezing? */
/*
* The almighty global cpu workqueues. nr_running is the only field
* which is expected to be used frequently by other cpus via
* try_to_wake_up(). Put it in a separate cacheline.
*/
static DEFINE_PER_CPU(struct global_cwq, global_cwq);
static DEFINE_PER_CPU_SHARED_ALIGNED(atomic_t, gcwq_nr_running);
/*
* Global cpu workqueue and nr_running counter for unbound gcwq. The
* gcwq is always online, has GCWQ_DISASSOCIATED set, and all its
* workers have WORKER_UNBOUND set.
*/
static struct global_cwq unbound_global_cwq;
static atomic_t unbound_gcwq_nr_running = ATOMIC_INIT(0); /* always 0 */
static int worker_thread(void *__worker);
static struct global_cwq *get_gcwq(unsigned int cpu)
{
if (cpu != WORK_CPU_UNBOUND)
return &per_cpu(global_cwq, cpu);
else
return &unbound_global_cwq;
}
static atomic_t *get_gcwq_nr_running(unsigned int cpu)
{
if (cpu != WORK_CPU_UNBOUND)
return &per_cpu(gcwq_nr_running, cpu);
else
return &unbound_gcwq_nr_running;
}
static struct cpu_workqueue_struct *get_cwq(unsigned int cpu,
struct workqueue_struct *wq)
{
if (!(wq->flags & WQ_UNBOUND)) {
if (likely(cpu < nr_cpu_ids)) {
#ifdef CONFIG_SMP
return per_cpu_ptr(wq->cpu_wq.pcpu, cpu);
#else
return wq->cpu_wq.single;
#endif
}
} else if (likely(cpu == WORK_CPU_UNBOUND))
return wq->cpu_wq.single;
return NULL;
}
static unsigned int work_color_to_flags(int color)
{
return color << WORK_STRUCT_COLOR_SHIFT;
}
static int get_work_color(struct work_struct *work)
{
return (*work_data_bits(work) >> WORK_STRUCT_COLOR_SHIFT) &
((1 << WORK_STRUCT_COLOR_BITS) - 1);
}
static int work_next_color(int color)
{
return (color + 1) % WORK_NR_COLORS;
}
/*
* A work's data points to the cwq with WORK_STRUCT_CWQ set while the
* work is on queue. Once execution starts, WORK_STRUCT_CWQ is
* cleared and the work data contains the cpu number it was last on.
*
* set_work_{cwq|cpu}() and clear_work_data() can be used to set the
* cwq, cpu or clear work->data. These functions should only be
* called while the work is owned - ie. while the PENDING bit is set.
*
* get_work_[g]cwq() can be used to obtain the gcwq or cwq
* corresponding to a work. gcwq is available once the work has been
* queued anywhere after initialization. cwq is available only from
* queueing until execution starts.
*/
static inline void set_work_data(struct work_struct *work, unsigned long data,
unsigned long flags)
{
BUG_ON(!work_pending(work));
atomic_long_set(&work->data, data | flags | work_static(work));
}
static void set_work_cwq(struct work_struct *work,
struct cpu_workqueue_struct *cwq,
unsigned long extra_flags)
{
set_work_data(work, (unsigned long)cwq,
WORK_STRUCT_PENDING | WORK_STRUCT_CWQ | extra_flags);
}
static void set_work_cpu(struct work_struct *work, unsigned int cpu)
{
set_work_data(work, cpu << WORK_STRUCT_FLAG_BITS, WORK_STRUCT_PENDING);
}
static void clear_work_data(struct work_struct *work)
{
set_work_data(work, WORK_STRUCT_NO_CPU, 0);
}
static struct cpu_workqueue_struct *get_work_cwq(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
if (data & WORK_STRUCT_CWQ)
return (void *)(data & WORK_STRUCT_WQ_DATA_MASK);
else
return NULL;
}
static struct global_cwq *get_work_gcwq(struct work_struct *work)
{
unsigned long data = atomic_long_read(&work->data);
unsigned int cpu;
if (data & WORK_STRUCT_CWQ)
return ((struct cpu_workqueue_struct *)
(data & WORK_STRUCT_WQ_DATA_MASK))->gcwq;
cpu = data >> WORK_STRUCT_FLAG_BITS;
if (cpu == WORK_CPU_NONE)
return NULL;
BUG_ON(cpu >= nr_cpu_ids && cpu != WORK_CPU_UNBOUND);
return get_gcwq(cpu);
}
/*
* Policy functions. These define the policies on how the global
* worker pool is managed. Unless noted otherwise, these functions
* assume that they're being called with gcwq->lock held.
*/
static bool __need_more_worker(struct global_cwq *gcwq)
{
return !atomic_read(get_gcwq_nr_running(gcwq->cpu)) ||
gcwq->flags & GCWQ_HIGHPRI_PENDING;
}
/*
* Need to wake up a worker? Called from anything but currently
* running workers.
*/
static bool need_more_worker(struct global_cwq *gcwq)
{
return !list_empty(&gcwq->worklist) && __need_more_worker(gcwq);
}
/* Can I start working? Called from busy but !running workers. */
static bool may_start_working(struct global_cwq *gcwq)
{
return gcwq->nr_idle;
}
/* Do I need to keep working? Called from currently running workers. */
static bool keep_working(struct global_cwq *gcwq)
{
atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
return !list_empty(&gcwq->worklist) &&
(atomic_read(nr_running) <= 1 ||
gcwq->flags & GCWQ_HIGHPRI_PENDING);
}
/* Do we need a new worker? Called from manager. */
static bool need_to_create_worker(struct global_cwq *gcwq)
{
return need_more_worker(gcwq) && !may_start_working(gcwq);
}
/* Do I need to be the manager? */
static bool need_to_manage_workers(struct global_cwq *gcwq)
{
return need_to_create_worker(gcwq) || gcwq->flags & GCWQ_MANAGE_WORKERS;
}
/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct global_cwq *gcwq)
{
bool managing = gcwq->flags & GCWQ_MANAGING_WORKERS;
int nr_idle = gcwq->nr_idle + managing; /* manager is considered idle */
int nr_busy = gcwq->nr_workers - nr_idle;
return nr_idle > 2 && (nr_idle - 2) * MAX_IDLE_WORKERS_RATIO >= nr_busy;
}
/*
* Wake up functions.
*/
/* Return the first worker. Safe with preemption disabled */
static struct worker *first_worker(struct global_cwq *gcwq)
{
if (unlikely(list_empty(&gcwq->idle_list)))
return NULL;
return list_first_entry(&gcwq->idle_list, struct worker, entry);
}
/**
* wake_up_worker - wake up an idle worker
* @gcwq: gcwq to wake worker for
*
* Wake up the first idle worker of @gcwq.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void wake_up_worker(struct global_cwq *gcwq)
{
struct worker *worker = first_worker(gcwq);
if (likely(worker))
wake_up_process(worker->task);
}
/**
* wq_worker_waking_up - a worker is waking up
* @task: task waking up
* @cpu: CPU @task is waking up to
*
* This function is called during try_to_wake_up() when a worker is
* being awoken.
*
* CONTEXT:
* spin_lock_irq(rq->lock)
*/
void wq_worker_waking_up(struct task_struct *task, unsigned int cpu)
{
struct worker *worker = kthread_data(task);
if (!(worker->flags & WORKER_NOT_RUNNING))
atomic_inc(get_gcwq_nr_running(cpu));
}
/**
* wq_worker_sleeping - a worker is going to sleep
* @task: task going to sleep
* @cpu: CPU in question, must be the current CPU number
*
* This function is called during schedule() when a busy worker is
* going to sleep. Worker on the same cpu can be woken up by
* returning pointer to its task.
*
* CONTEXT:
* spin_lock_irq(rq->lock)
*
* RETURNS:
* Worker task on @cpu to wake up, %NULL if none.
*/
struct task_struct *wq_worker_sleeping(struct task_struct *task,
unsigned int cpu)
{
struct worker *worker = kthread_data(task), *to_wakeup = NULL;
struct global_cwq *gcwq = get_gcwq(cpu);
atomic_t *nr_running = get_gcwq_nr_running(cpu);
if (worker->flags & WORKER_NOT_RUNNING)
return NULL;
/* this can only happen on the local cpu */
BUG_ON(cpu != raw_smp_processor_id());
/*
* The counterpart of the following dec_and_test, implied mb,
* worklist not empty test sequence is in insert_work().
* Please read comment there.
*
* NOT_RUNNING is clear. This means that trustee is not in
* charge and we're running on the local cpu w/ rq lock held
* and preemption disabled, which in turn means that none else
* could be manipulating idle_list, so dereferencing idle_list
* without gcwq lock is safe.
*/
if (atomic_dec_and_test(nr_running) && !list_empty(&gcwq->worklist))
to_wakeup = first_worker(gcwq);
return to_wakeup ? to_wakeup->task : NULL;
}
/**
* worker_set_flags - set worker flags and adjust nr_running accordingly
* @worker: self
* @flags: flags to set
* @wakeup: wakeup an idle worker if necessary
*
* Set @flags in @worker->flags and adjust nr_running accordingly. If
* nr_running becomes zero and @wakeup is %true, an idle worker is
* woken up.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock)
*/
static inline void worker_set_flags(struct worker *worker, unsigned int flags,
bool wakeup)
{
struct global_cwq *gcwq = worker->gcwq;
WARN_ON_ONCE(worker->task != current);
/*
* If transitioning into NOT_RUNNING, adjust nr_running and
* wake up an idle worker as necessary if requested by
* @wakeup.
*/
if ((flags & WORKER_NOT_RUNNING) &&
!(worker->flags & WORKER_NOT_RUNNING)) {
atomic_t *nr_running = get_gcwq_nr_running(gcwq->cpu);
if (wakeup) {
if (atomic_dec_and_test(nr_running) &&
!list_empty(&gcwq->worklist))
wake_up_worker(gcwq);
} else
atomic_dec(nr_running);
}
worker->flags |= flags;
}
/**
* worker_clr_flags - clear worker flags and adjust nr_running accordingly
* @worker: self
* @flags: flags to clear
*
* Clear @flags in @worker->flags and adjust nr_running accordingly.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock)
*/
static inline void worker_clr_flags(struct worker *worker, unsigned int flags)
{
struct global_cwq *gcwq = worker->gcwq;
unsigned int oflags = worker->flags;
WARN_ON_ONCE(worker->task != current);
worker->flags &= ~flags;
/*
* If transitioning out of NOT_RUNNING, increment nr_running. Note
* that the nested NOT_RUNNING is not a noop. NOT_RUNNING is mask
* of multiple flags, not a single flag.
*/
if ((flags & WORKER_NOT_RUNNING) && (oflags & WORKER_NOT_RUNNING))
if (!(worker->flags & WORKER_NOT_RUNNING))
atomic_inc(get_gcwq_nr_running(gcwq->cpu));
}
/**
* busy_worker_head - return the busy hash head for a work
* @gcwq: gcwq of interest
* @work: work to be hashed
*
* Return hash head of @gcwq for @work.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*
* RETURNS:
* Pointer to the hash head.
*/
static struct hlist_head *busy_worker_head(struct global_cwq *gcwq,
struct work_struct *work)
{
const int base_shift = ilog2(sizeof(struct work_struct));
unsigned long v = (unsigned long)work;
/* simple shift and fold hash, do we need something better? */
v >>= base_shift;
v += v >> BUSY_WORKER_HASH_ORDER;
v &= BUSY_WORKER_HASH_MASK;
return &gcwq->busy_hash[v];
}
/**
* __find_worker_executing_work - find worker which is executing a work
* @gcwq: gcwq of interest
* @bwh: hash head as returned by busy_worker_head()
* @work: work to find worker for
*
* Find a worker which is executing @work on @gcwq. @bwh should be
* the hash head obtained by calling busy_worker_head() with the same
* work.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*
* RETURNS:
* Pointer to worker which is executing @work if found, NULL
* otherwise.
*/
static struct worker *__find_worker_executing_work(struct global_cwq *gcwq,
struct hlist_head *bwh,
struct work_struct *work)
{
struct worker *worker;
struct hlist_node *tmp;
hlist_for_each_entry(worker, tmp, bwh, hentry)
if (worker->current_work == work)
return worker;
return NULL;
}
/**
* find_worker_executing_work - find worker which is executing a work
* @gcwq: gcwq of interest
* @work: work to find worker for
*
* Find a worker which is executing @work on @gcwq. This function is
* identical to __find_worker_executing_work() except that this
* function calculates @bwh itself.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*
* RETURNS:
* Pointer to worker which is executing @work if found, NULL
* otherwise.
*/
static struct worker *find_worker_executing_work(struct global_cwq *gcwq,
struct work_struct *work)
{
return __find_worker_executing_work(gcwq, busy_worker_head(gcwq, work),
work);
}
/**
* gcwq_determine_ins_pos - find insertion position
* @gcwq: gcwq of interest
* @cwq: cwq a work is being queued for
*
* A work for @cwq is about to be queued on @gcwq, determine insertion
* position for the work. If @cwq is for HIGHPRI wq, the work is
* queued at the head of the queue but in FIFO order with respect to
* other HIGHPRI works; otherwise, at the end of the queue. This
* function also sets GCWQ_HIGHPRI_PENDING flag to hint @gcwq that
* there are HIGHPRI works pending.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*
* RETURNS:
* Pointer to inserstion position.
*/
static inline struct list_head *gcwq_determine_ins_pos(struct global_cwq *gcwq,
struct cpu_workqueue_struct *cwq)
{
struct work_struct *twork;
if (likely(!(cwq->wq->flags & WQ_HIGHPRI)))
return &gcwq->worklist;
list_for_each_entry(twork, &gcwq->worklist, entry) {
struct cpu_workqueue_struct *tcwq = get_work_cwq(twork);
if (!(tcwq->wq->flags & WQ_HIGHPRI))
break;
}
gcwq->flags |= GCWQ_HIGHPRI_PENDING;
return &twork->entry;
}
/**
* insert_work - insert a work into gcwq
* @cwq: cwq @work belongs to
* @work: work to insert
* @head: insertion point
* @extra_flags: extra WORK_STRUCT_* flags to set
*
* Insert @work which belongs to @cwq into @gcwq after @head.
* @extra_flags is or'd to work_struct flags.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void insert_work(struct cpu_workqueue_struct *cwq,
struct work_struct *work, struct list_head *head,
unsigned int extra_flags)
{
struct global_cwq *gcwq = cwq->gcwq;
/* we own @work, set data and link */
set_work_cwq(work, cwq, extra_flags);
/*
* Ensure that we get the right work->data if we see the
* result of list_add() below, see try_to_grab_pending().
*/
smp_wmb();
list_add_tail(&work->entry, head);
/*
* Ensure either worker_sched_deactivated() sees the above
* list_add_tail() or we see zero nr_running to avoid workers
* lying around lazily while there are works to be processed.
*/
smp_mb();
if (__need_more_worker(gcwq))
wake_up_worker(gcwq);
}
/*
* Test whether @work is being queued from another work executing on the
* same workqueue. This is rather expensive and should only be used from
* cold paths.
*/
static bool is_chained_work(struct workqueue_struct *wq)
{
unsigned long flags;
unsigned int cpu;
for_each_gcwq_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct worker *worker;
struct hlist_node *pos;
int i;
spin_lock_irqsave(&gcwq->lock, flags);
for_each_busy_worker(worker, i, pos, gcwq) {
if (worker->task != current)
continue;
spin_unlock_irqrestore(&gcwq->lock, flags);
/*
* I'm @worker, no locking necessary. See if @work
* is headed to the same workqueue.
*/
return worker->current_cwq->wq == wq;
}
spin_unlock_irqrestore(&gcwq->lock, flags);
}
return false;
}
static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
struct global_cwq *gcwq;
struct cpu_workqueue_struct *cwq;
struct list_head *worklist;
unsigned int work_flags;
unsigned long flags;
debug_work_activate(work);
/* if dying, only works from the same workqueue are allowed */
if (unlikely(wq->flags & WQ_DRAINING) &&
WARN_ON_ONCE(!is_chained_work(wq)))
return;
/* determine gcwq to use */
if (!(wq->flags & WQ_UNBOUND)) {
struct global_cwq *last_gcwq;
if (unlikely(cpu == WORK_CPU_UNBOUND))
cpu = raw_smp_processor_id();
/*
* It's multi cpu. If @wq is non-reentrant and @work
* was previously on a different cpu, it might still
* be running there, in which case the work needs to
* be queued on that cpu to guarantee non-reentrance.
*/
gcwq = get_gcwq(cpu);
if (wq->flags & WQ_NON_REENTRANT &&
(last_gcwq = get_work_gcwq(work)) && last_gcwq != gcwq) {
struct worker *worker;
spin_lock_irqsave(&last_gcwq->lock, flags);
worker = find_worker_executing_work(last_gcwq, work);
if (worker && worker->current_cwq->wq == wq)
gcwq = last_gcwq;
else {
/* meh... not running there, queue here */
spin_unlock_irqrestore(&last_gcwq->lock, flags);
spin_lock_irqsave(&gcwq->lock, flags);
}
} else
spin_lock_irqsave(&gcwq->lock, flags);
} else {
gcwq = get_gcwq(WORK_CPU_UNBOUND);
spin_lock_irqsave(&gcwq->lock, flags);
}
/* gcwq determined, get cwq and queue */
cwq = get_cwq(gcwq->cpu, wq);
trace_workqueue_queue_work(cpu, cwq, work);
BUG_ON(!list_empty(&work->entry));
cwq->nr_in_flight[cwq->work_color]++;
work_flags = work_color_to_flags(cwq->work_color);
if (likely(cwq->nr_active < cwq->max_active)) {
trace_workqueue_activate_work(work);
cwq->nr_active++;
worklist = gcwq_determine_ins_pos(gcwq, cwq);
} else {
work_flags |= WORK_STRUCT_DELAYED;
worklist = &cwq->delayed_works;
}
insert_work(cwq, work, worklist, work_flags);
spin_unlock_irqrestore(&gcwq->lock, flags);
}
/**
* queue_work - queue work on a workqueue
* @wq: workqueue to use
* @work: work to queue
*
* Returns 0 if @work was already on a queue, non-zero otherwise.
*
* We queue the work to the CPU on which it was submitted, but if the CPU dies
* it can be processed by another CPU.
*/
int queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
int ret;
ret = queue_work_on(get_cpu(), wq, work);
put_cpu();
return ret;
}
EXPORT_SYMBOL_GPL(queue_work);
/**
* queue_work_on - queue work on specific cpu
* @cpu: CPU number to execute work on
* @wq: workqueue to use
* @work: work to queue
*
* Returns 0 if @work was already on a queue, non-zero otherwise.
*
* We queue the work to a specific CPU, the caller must ensure it
* can't go away.
*/
int
queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
{
int ret = 0;
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
__queue_work(cpu, wq, work);
ret = 1;
}
return ret;
}
EXPORT_SYMBOL_GPL(queue_work_on);
static void delayed_work_timer_fn(unsigned long __data)
{
struct delayed_work *dwork = (struct delayed_work *)__data;
struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);
__queue_work(smp_processor_id(), cwq->wq, &dwork->work);
}
/**
* queue_delayed_work - queue work on a workqueue after delay
* @wq: workqueue to use
* @dwork: delayable work to queue
* @delay: number of jiffies to wait before queueing
*
* Returns 0 if @work was already on a queue, non-zero otherwise.
*/
int queue_delayed_work(struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay)
{
if (delay == 0)
return queue_work(wq, &dwork->work);
return queue_delayed_work_on(-1, wq, dwork, delay);
}
EXPORT_SYMBOL_GPL(queue_delayed_work);
/**
* queue_delayed_work_on - queue work on specific CPU after delay
* @cpu: CPU number to execute work on
* @wq: workqueue to use
* @dwork: work to queue
* @delay: number of jiffies to wait before queueing
*
* Returns 0 if @work was already on a queue, non-zero otherwise.
*/
int queue_delayed_work_on(int cpu, struct workqueue_struct *wq,
struct delayed_work *dwork, unsigned long delay)
{
int ret = 0;
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work))) {
unsigned int lcpu;
BUG_ON(timer_pending(timer));
BUG_ON(!list_empty(&work->entry));
timer_stats_timer_set_start_info(&dwork->timer);
/*
* This stores cwq for the moment, for the timer_fn.
* Note that the work's gcwq is preserved to allow
* reentrance detection for delayed works.
*/
if (!(wq->flags & WQ_UNBOUND)) {
struct global_cwq *gcwq = get_work_gcwq(work);
if (gcwq && gcwq->cpu != WORK_CPU_UNBOUND)
lcpu = gcwq->cpu;
else
lcpu = raw_smp_processor_id();
} else
lcpu = WORK_CPU_UNBOUND;
set_work_cwq(work, get_cwq(lcpu, wq), 0);
timer->expires = jiffies + delay;
timer->data = (unsigned long)dwork;
timer->function = delayed_work_timer_fn;
if (unlikely(cpu >= 0))
add_timer_on(timer, cpu);
else
add_timer(timer);
ret = 1;
}
return ret;
}
EXPORT_SYMBOL_GPL(queue_delayed_work_on);
/**
* worker_enter_idle - enter idle state
* @worker: worker which is entering idle state
*
* @worker is entering idle state. Update stats and idle timer if
* necessary.
*
* LOCKING:
* spin_lock_irq(gcwq->lock).
*/
static void worker_enter_idle(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
BUG_ON(worker->flags & WORKER_IDLE);
BUG_ON(!list_empty(&worker->entry) &&
(worker->hentry.next || worker->hentry.pprev));
/* can't use worker_set_flags(), also called from start_worker() */
worker->flags |= WORKER_IDLE;
gcwq->nr_idle++;
worker->last_active = jiffies;
/* idle_list is LIFO */
list_add(&worker->entry, &gcwq->idle_list);
if (likely(!(worker->flags & WORKER_ROGUE))) {
if (too_many_workers(gcwq) && !timer_pending(&gcwq->idle_timer))
mod_timer(&gcwq->idle_timer,
jiffies + IDLE_WORKER_TIMEOUT);
} else
wake_up_all(&gcwq->trustee_wait);
/* sanity check nr_running */
WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle &&
atomic_read(get_gcwq_nr_running(gcwq->cpu)));
}
/**
* worker_leave_idle - leave idle state
* @worker: worker which is leaving idle state
*
* @worker is leaving idle state. Update stats.
*
* LOCKING:
* spin_lock_irq(gcwq->lock).
*/
static void worker_leave_idle(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
BUG_ON(!(worker->flags & WORKER_IDLE));
worker_clr_flags(worker, WORKER_IDLE);
gcwq->nr_idle--;
list_del_init(&worker->entry);
}
/**
* worker_maybe_bind_and_lock - bind worker to its cpu if possible and lock gcwq
* @worker: self
*
* Works which are scheduled while the cpu is online must at least be
* scheduled to a worker which is bound to the cpu so that if they are
* flushed from cpu callbacks while cpu is going down, they are
* guaranteed to execute on the cpu.
*
* This function is to be used by rogue workers and rescuers to bind
* themselves to the target cpu and may race with cpu going down or
* coming online. kthread_bind() can't be used because it may put the
* worker to already dead cpu and set_cpus_allowed_ptr() can't be used
* verbatim as it's best effort and blocking and gcwq may be
* [dis]associated in the meantime.
*
* This function tries set_cpus_allowed() and locks gcwq and verifies
* the binding against GCWQ_DISASSOCIATED which is set during
* CPU_DYING and cleared during CPU_ONLINE, so if the worker enters
* idle state or fetches works without dropping lock, it can guarantee
* the scheduling requirement described in the first paragraph.
*
* CONTEXT:
* Might sleep. Called without any lock but returns with gcwq->lock
* held.
*
* RETURNS:
* %true if the associated gcwq is online (@worker is successfully
* bound), %false if offline.
*/
static bool worker_maybe_bind_and_lock(struct worker *worker)
__acquires(&gcwq->lock)
{
struct global_cwq *gcwq = worker->gcwq;
struct task_struct *task = worker->task;
while (true) {
/*
* The following call may fail, succeed or succeed
* without actually migrating the task to the cpu if
* it races with cpu hotunplug operation. Verify
* against GCWQ_DISASSOCIATED.
*/
if (!(gcwq->flags & GCWQ_DISASSOCIATED))
set_cpus_allowed_ptr(task, get_cpu_mask(gcwq->cpu));
spin_lock_irq(&gcwq->lock);
if (gcwq->flags & GCWQ_DISASSOCIATED)
return false;
if (task_cpu(task) == gcwq->cpu &&
cpumask_equal(&current->cpus_allowed,
get_cpu_mask(gcwq->cpu)))
return true;
spin_unlock_irq(&gcwq->lock);
/*
* We've raced with CPU hot[un]plug. Give it a breather
* and retry migration. cond_resched() is required here;
* otherwise, we might deadlock against cpu_stop trying to
* bring down the CPU on non-preemptive kernel.
*/
cpu_relax();
cond_resched();
}
}
/*
* Function for worker->rebind_work used to rebind rogue busy workers
* to the associated cpu which is coming back online. This is
* scheduled by cpu up but can race with other cpu hotplug operations
* and may be executed twice without intervening cpu down.
*/
static void worker_rebind_fn(struct work_struct *work)
{
struct worker *worker = container_of(work, struct worker, rebind_work);
struct global_cwq *gcwq = worker->gcwq;
if (worker_maybe_bind_and_lock(worker))
worker_clr_flags(worker, WORKER_REBIND);
spin_unlock_irq(&gcwq->lock);
}
static struct worker *alloc_worker(void)
{
struct worker *worker;
worker = kzalloc(sizeof(*worker), GFP_KERNEL);
if (worker) {
INIT_LIST_HEAD(&worker->entry);
INIT_LIST_HEAD(&worker->scheduled);
INIT_WORK(&worker->rebind_work, worker_rebind_fn);
/* on creation a worker is in !idle && prep state */
worker->flags = WORKER_PREP;
}
return worker;
}
/**
* create_worker - create a new workqueue worker
* @gcwq: gcwq the new worker will belong to
* @bind: whether to set affinity to @cpu or not
*
* Create a new worker which is bound to @gcwq. The returned worker
* can be started by calling start_worker() or destroyed using
* destroy_worker().
*
* CONTEXT:
* Might sleep. Does GFP_KERNEL allocations.
*
* RETURNS:
* Pointer to the newly created worker.
*/
static struct worker *create_worker(struct global_cwq *gcwq, bool bind)
{
bool on_unbound_cpu = gcwq->cpu == WORK_CPU_UNBOUND;
struct worker *worker = NULL;
int id = -1;
spin_lock_irq(&gcwq->lock);
while (ida_get_new(&gcwq->worker_ida, &id)) {
spin_unlock_irq(&gcwq->lock);
if (!ida_pre_get(&gcwq->worker_ida, GFP_KERNEL))
goto fail;
spin_lock_irq(&gcwq->lock);
}
spin_unlock_irq(&gcwq->lock);
worker = alloc_worker();
if (!worker)
goto fail;
worker->gcwq = gcwq;
worker->id = id;
if (!on_unbound_cpu)
worker->task = kthread_create_on_node(worker_thread,
worker,
cpu_to_node(gcwq->cpu),
"kworker/%u:%d", gcwq->cpu, id);
else
worker->task = kthread_create(worker_thread, worker,
"kworker/u:%d", id);
if (IS_ERR(worker->task))
goto fail;
/*
* A rogue worker will become a regular one if CPU comes
* online later on. Make sure every worker has
* PF_THREAD_BOUND set.
*/
if (bind && !on_unbound_cpu)
kthread_bind(worker->task, gcwq->cpu);
else {
worker->task->flags |= PF_THREAD_BOUND;
if (on_unbound_cpu)
worker->flags |= WORKER_UNBOUND;
}
return worker;
fail:
if (id >= 0) {
spin_lock_irq(&gcwq->lock);
ida_remove(&gcwq->worker_ida, id);
spin_unlock_irq(&gcwq->lock);
}
kfree(worker);
return NULL;
}
/**
* start_worker - start a newly created worker
* @worker: worker to start
*
* Make the gcwq aware of @worker and start it.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void start_worker(struct worker *worker)
{
worker->flags |= WORKER_STARTED;
worker->gcwq->nr_workers++;
worker_enter_idle(worker);
wake_up_process(worker->task);
}
/**
* destroy_worker - destroy a workqueue worker
* @worker: worker to be destroyed
*
* Destroy @worker and adjust @gcwq stats accordingly.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which is released and regrabbed.
*/
static void destroy_worker(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
int id = worker->id;
/* sanity check frenzy */
BUG_ON(worker->current_work);
BUG_ON(!list_empty(&worker->scheduled));
if (worker->flags & WORKER_STARTED)
gcwq->nr_workers--;
if (worker->flags & WORKER_IDLE)
gcwq->nr_idle--;
list_del_init(&worker->entry);
worker->flags |= WORKER_DIE;
spin_unlock_irq(&gcwq->lock);
kthread_stop(worker->task);
kfree(worker);
spin_lock_irq(&gcwq->lock);
ida_remove(&gcwq->worker_ida, id);
}
static void idle_worker_timeout(unsigned long __gcwq)
{
struct global_cwq *gcwq = (void *)__gcwq;
spin_lock_irq(&gcwq->lock);
if (too_many_workers(gcwq)) {
struct worker *worker;
unsigned long expires;
/* idle_list is kept in LIFO order, check the last one */
worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
expires = worker->last_active + IDLE_WORKER_TIMEOUT;
if (time_before(jiffies, expires))
mod_timer(&gcwq->idle_timer, expires);
else {
/* it's been idle for too long, wake up manager */
gcwq->flags |= GCWQ_MANAGE_WORKERS;
wake_up_worker(gcwq);
}
}
spin_unlock_irq(&gcwq->lock);
}
static bool send_mayday(struct work_struct *work)
{
struct cpu_workqueue_struct *cwq = get_work_cwq(work);
struct workqueue_struct *wq = cwq->wq;
unsigned int cpu;
if (!(wq->flags & WQ_RESCUER))
return false;
/* mayday mayday mayday */
cpu = cwq->gcwq->cpu;
/* WORK_CPU_UNBOUND can't be set in cpumask, use cpu 0 instead */
if (cpu == WORK_CPU_UNBOUND)
cpu = 0;
if (!mayday_test_and_set_cpu(cpu, wq->mayday_mask))
wake_up_process(wq->rescuer->task);
return true;
}
static void gcwq_mayday_timeout(unsigned long __gcwq)
{
struct global_cwq *gcwq = (void *)__gcwq;
struct work_struct *work;
spin_lock_irq(&gcwq->lock);
if (need_to_create_worker(gcwq)) {
/*
* We've been trying to create a new worker but
* haven't been successful. We might be hitting an
* allocation deadlock. Send distress signals to
* rescuers.
*/
list_for_each_entry(work, &gcwq->worklist, entry)
send_mayday(work);
}
spin_unlock_irq(&gcwq->lock);
mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INTERVAL);
}
/**
* maybe_create_worker - create a new worker if necessary
* @gcwq: gcwq to create a new worker for
*
* Create a new worker for @gcwq if necessary. @gcwq is guaranteed to
* have at least one idle worker on return from this function. If
* creating a new worker takes longer than MAYDAY_INTERVAL, mayday is
* sent to all rescuers with works scheduled on @gcwq to resolve
* possible allocation deadlock.
*
* On return, need_to_create_worker() is guaranteed to be false and
* may_start_working() true.
*
* LOCKING:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. Does GFP_KERNEL allocations. Called only from
* manager.
*
* RETURNS:
* false if no action was taken and gcwq->lock stayed locked, true
* otherwise.
*/
static bool maybe_create_worker(struct global_cwq *gcwq)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
if (!need_to_create_worker(gcwq))
return false;
restart:
spin_unlock_irq(&gcwq->lock);
/* if we don't make progress in MAYDAY_INITIAL_TIMEOUT, call for help */
mod_timer(&gcwq->mayday_timer, jiffies + MAYDAY_INITIAL_TIMEOUT);
while (true) {
struct worker *worker;
worker = create_worker(gcwq, true);
if (worker) {
del_timer_sync(&gcwq->mayday_timer);
spin_lock_irq(&gcwq->lock);
start_worker(worker);
BUG_ON(need_to_create_worker(gcwq));
return true;
}
if (!need_to_create_worker(gcwq))
break;
__set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(CREATE_COOLDOWN);
if (!need_to_create_worker(gcwq))
break;
}
del_timer_sync(&gcwq->mayday_timer);
spin_lock_irq(&gcwq->lock);
if (need_to_create_worker(gcwq))
goto restart;
return true;
}
/**
* maybe_destroy_worker - destroy workers which have been idle for a while
* @gcwq: gcwq to destroy workers for
*
* Destroy @gcwq workers which have been idle for longer than
* IDLE_WORKER_TIMEOUT.
*
* LOCKING:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. Called only from manager.
*
* RETURNS:
* false if no action was taken and gcwq->lock stayed locked, true
* otherwise.
*/
static bool maybe_destroy_workers(struct global_cwq *gcwq)
{
bool ret = false;
while (too_many_workers(gcwq)) {
struct worker *worker;
unsigned long expires;
worker = list_entry(gcwq->idle_list.prev, struct worker, entry);
expires = worker->last_active + IDLE_WORKER_TIMEOUT;
if (time_before(jiffies, expires)) {
mod_timer(&gcwq->idle_timer, expires);
break;
}
destroy_worker(worker);
ret = true;
}
return ret;
}
/**
* manage_workers - manage worker pool
* @worker: self
*
* Assume the manager role and manage gcwq worker pool @worker belongs
* to. At any given time, there can be only zero or one manager per
* gcwq. The exclusion is handled automatically by this function.
*
* The caller can safely start processing works on false return. On
* true return, it's guaranteed that need_to_create_worker() is false
* and may_start_working() is true.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. Does GFP_KERNEL allocations.
*
* RETURNS:
* false if no action was taken and gcwq->lock stayed locked, true if
* some action was taken.
*/
static bool manage_workers(struct worker *worker)
{
struct global_cwq *gcwq = worker->gcwq;
bool ret = false;
if (gcwq->flags & GCWQ_MANAGING_WORKERS)
return ret;
gcwq->flags &= ~GCWQ_MANAGE_WORKERS;
gcwq->flags |= GCWQ_MANAGING_WORKERS;
/*
* Destroy and then create so that may_start_working() is true
* on return.
*/
ret |= maybe_destroy_workers(gcwq);
ret |= maybe_create_worker(gcwq);
gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
/*
* The trustee might be waiting to take over the manager
* position, tell it we're done.
*/
if (unlikely(gcwq->trustee))
wake_up_all(&gcwq->trustee_wait);
return ret;
}
/**
* move_linked_works - move linked works to a list
* @work: start of series of works to be scheduled
* @head: target list to append @work to
* @nextp: out paramter for nested worklist walking
*
* Schedule linked works starting from @work to @head. Work series to
* be scheduled starts at @work and includes any consecutive work with
* WORK_STRUCT_LINKED set in its predecessor.
*
* If @nextp is not NULL, it's updated to point to the next work of
* the last scheduled work. This allows move_linked_works() to be
* nested inside outer list_for_each_entry_safe().
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void move_linked_works(struct work_struct *work, struct list_head *head,
struct work_struct **nextp)
{
struct work_struct *n;
/*
* Linked worklist will always end before the end of the list,
* use NULL for list head.
*/
list_for_each_entry_safe_from(work, n, NULL, entry) {
list_move_tail(&work->entry, head);
if (!(*work_data_bits(work) & WORK_STRUCT_LINKED))
break;
}
/*
* If we're already inside safe list traversal and have moved
* multiple works to the scheduled queue, the next position
* needs to be updated.
*/
if (nextp)
*nextp = n;
}
static void cwq_activate_first_delayed(struct cpu_workqueue_struct *cwq)
{
struct work_struct *work = list_first_entry(&cwq->delayed_works,
struct work_struct, entry);
struct list_head *pos = gcwq_determine_ins_pos(cwq->gcwq, cwq);
trace_workqueue_activate_work(work);
move_linked_works(work, pos, NULL);
__clear_bit(WORK_STRUCT_DELAYED_BIT, work_data_bits(work));
cwq->nr_active++;
}
/**
* cwq_dec_nr_in_flight - decrement cwq's nr_in_flight
* @cwq: cwq of interest
* @color: color of work which left the queue
* @delayed: for a delayed work
*
* A work either has completed or is removed from pending queue,
* decrement nr_in_flight of its cwq and handle workqueue flushing.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void cwq_dec_nr_in_flight(struct cpu_workqueue_struct *cwq, int color,
bool delayed)
{
/* ignore uncolored works */
if (color == WORK_NO_COLOR)
return;
cwq->nr_in_flight[color]--;
if (!delayed) {
cwq->nr_active--;
if (!list_empty(&cwq->delayed_works)) {
/* one down, submit a delayed one */
if (cwq->nr_active < cwq->max_active)
cwq_activate_first_delayed(cwq);
}
}
/* is flush in progress and are we at the flushing tip? */
if (likely(cwq->flush_color != color))
return;
/* are there still in-flight works? */
if (cwq->nr_in_flight[color])
return;
/* this cwq is done, clear flush_color */
cwq->flush_color = -1;
/*
* If this was the last cwq, wake up the first flusher. It
* will handle the rest.
*/
if (atomic_dec_and_test(&cwq->wq->nr_cwqs_to_flush))
complete(&cwq->wq->first_flusher->done);
}
/**
* process_one_work - process single work
* @worker: self
* @work: work to process
*
* Process @work. This function contains all the logics necessary to
* process a single work including synchronization against and
* interaction with other workers on the same cpu, queueing and
* flushing. As long as context requirement is met, any worker can
* call this function to process a work.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which is released and regrabbed.
*/
static void process_one_work(struct worker *worker, struct work_struct *work)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
struct cpu_workqueue_struct *cwq = get_work_cwq(work);
struct global_cwq *gcwq = cwq->gcwq;
struct hlist_head *bwh = busy_worker_head(gcwq, work);
bool cpu_intensive = cwq->wq->flags & WQ_CPU_INTENSIVE;
work_func_t f = work->func;
int work_color;
struct worker *collision;
#ifdef CONFIG_LOCKDEP
/*
* It is permissible to free the struct work_struct from
* inside the function that is called from it, this we need to
* take into account for lockdep too. To avoid bogus "held
* lock freed" warnings as well as problems when looking into
* work->lockdep_map, make a copy and use that here.
*/
struct lockdep_map lockdep_map = work->lockdep_map;
#endif
/*
* A single work shouldn't be executed concurrently by
* multiple workers on a single cpu. Check whether anyone is
* already processing the work. If so, defer the work to the
* currently executing one.
*/
collision = __find_worker_executing_work(gcwq, bwh, work);
if (unlikely(collision)) {
move_linked_works(work, &collision->scheduled, NULL);
return;
}
/* claim and process */
debug_work_deactivate(work);
hlist_add_head(&worker->hentry, bwh);
worker->current_work = work;
worker->current_cwq = cwq;
work_color = get_work_color(work);
/* record the current cpu number in the work data and dequeue */
set_work_cpu(work, gcwq->cpu);
list_del_init(&work->entry);
/*
* If HIGHPRI_PENDING, check the next work, and, if HIGHPRI,
* wake up another worker; otherwise, clear HIGHPRI_PENDING.
*/
if (unlikely(gcwq->flags & GCWQ_HIGHPRI_PENDING)) {
struct work_struct *nwork = list_first_entry(&gcwq->worklist,
struct work_struct, entry);
if (!list_empty(&gcwq->worklist) &&
get_work_cwq(nwork)->wq->flags & WQ_HIGHPRI)
wake_up_worker(gcwq);
else
gcwq->flags &= ~GCWQ_HIGHPRI_PENDING;
}
/*
* CPU intensive works don't participate in concurrency
* management. They're the scheduler's responsibility.
*/
if (unlikely(cpu_intensive))
worker_set_flags(worker, WORKER_CPU_INTENSIVE, true);
spin_unlock_irq(&gcwq->lock);
work_clear_pending(work);
lock_map_acquire_read(&cwq->wq->lockdep_map);
lock_map_acquire(&lockdep_map);
trace_workqueue_execute_start(work);
f(work);
/*
* While we must be careful to not use "work" after this, the trace
* point will only record its address.
*/
trace_workqueue_execute_end(work);
lock_map_release(&lockdep_map);
lock_map_release(&cwq->wq->lockdep_map);
if (unlikely(in_atomic() || lockdep_depth(current) > 0)) {
printk(KERN_ERR "BUG: workqueue leaked lock or atomic: "
"%s/0x%08x/%d\n",
current->comm, preempt_count(), task_pid_nr(current));
printk(KERN_ERR " last function: ");
print_symbol("%s\n", (unsigned long)f);
debug_show_held_locks(current);
dump_stack();
}
spin_lock_irq(&gcwq->lock);
/* clear cpu intensive status */
if (unlikely(cpu_intensive))
worker_clr_flags(worker, WORKER_CPU_INTENSIVE);
/* we're done with it, release */
hlist_del_init(&worker->hentry);
worker->current_work = NULL;
worker->current_cwq = NULL;
cwq_dec_nr_in_flight(cwq, work_color, false);
}
/**
* process_scheduled_works - process scheduled works
* @worker: self
*
* Process all scheduled works. Please note that the scheduled list
* may change while processing a work, so this function repeatedly
* fetches a work from the top and executes it.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times.
*/
static void process_scheduled_works(struct worker *worker)
{
while (!list_empty(&worker->scheduled)) {
struct work_struct *work = list_first_entry(&worker->scheduled,
struct work_struct, entry);
process_one_work(worker, work);
}
}
/**
* worker_thread - the worker thread function
* @__worker: self
*
* The gcwq worker thread function. There's a single dynamic pool of
* these per each cpu. These workers process all works regardless of
* their specific target workqueue. The only exception is works which
* belong to workqueues with a rescuer which will be explained in
* rescuer_thread().
*/
static int worker_thread(void *__worker)
{
struct worker *worker = __worker;
struct global_cwq *gcwq = worker->gcwq;
/* tell the scheduler that this is a workqueue worker */
worker->task->flags |= PF_WQ_WORKER;
woke_up:
spin_lock_irq(&gcwq->lock);
/* DIE can be set only while we're idle, checking here is enough */
if (worker->flags & WORKER_DIE) {
spin_unlock_irq(&gcwq->lock);
worker->task->flags &= ~PF_WQ_WORKER;
return 0;
}
worker_leave_idle(worker);
recheck:
/* no more worker necessary? */
if (!need_more_worker(gcwq))
goto sleep;
/* do we need to manage? */
if (unlikely(!may_start_working(gcwq)) && manage_workers(worker))
goto recheck;
/*
* ->scheduled list can only be filled while a worker is
* preparing to process a work or actually processing it.
* Make sure nobody diddled with it while I was sleeping.
*/
BUG_ON(!list_empty(&worker->scheduled));
/*
* When control reaches this point, we're guaranteed to have
* at least one idle worker or that someone else has already
* assumed the manager role.
*/
worker_clr_flags(worker, WORKER_PREP);
do {
struct work_struct *work =
list_first_entry(&gcwq->worklist,
struct work_struct, entry);
if (likely(!(*work_data_bits(work) & WORK_STRUCT_LINKED))) {
/* optimization path, not strictly necessary */
process_one_work(worker, work);
if (unlikely(!list_empty(&worker->scheduled)))
process_scheduled_works(worker);
} else {
move_linked_works(work, &worker->scheduled, NULL);
process_scheduled_works(worker);
}
} while (keep_working(gcwq));
worker_set_flags(worker, WORKER_PREP, false);
sleep:
if (unlikely(need_to_manage_workers(gcwq)) && manage_workers(worker))
goto recheck;
/*
* gcwq->lock is held and there's no work to process and no
* need to manage, sleep. Workers are woken up only while
* holding gcwq->lock or from local cpu, so setting the
* current state before releasing gcwq->lock is enough to
* prevent losing any event.
*/
worker_enter_idle(worker);
__set_current_state(TASK_INTERRUPTIBLE);
spin_unlock_irq(&gcwq->lock);
schedule();
goto woke_up;
}
/**
* rescuer_thread - the rescuer thread function
* @__wq: the associated workqueue
*
* Workqueue rescuer thread function. There's one rescuer for each
* workqueue which has WQ_RESCUER set.
*
* Regular work processing on a gcwq may block trying to create a new
* worker which uses GFP_KERNEL allocation which has slight chance of
* developing into deadlock if some works currently on the same queue
* need to be processed to satisfy the GFP_KERNEL allocation. This is
* the problem rescuer solves.
*
* When such condition is possible, the gcwq summons rescuers of all
* workqueues which have works queued on the gcwq and let them process
* those works so that forward progress can be guaranteed.
*
* This should happen rarely.
*/
static int rescuer_thread(void *__wq)
{
struct workqueue_struct *wq = __wq;
struct worker *rescuer = wq->rescuer;
struct list_head *scheduled = &rescuer->scheduled;
bool is_unbound = wq->flags & WQ_UNBOUND;
unsigned int cpu;
set_user_nice(current, RESCUER_NICE_LEVEL);
repeat:
set_current_state(TASK_INTERRUPTIBLE);
if (kthread_should_stop())
return 0;
/*
* See whether any cpu is asking for help. Unbounded
* workqueues use cpu 0 in mayday_mask for CPU_UNBOUND.
*/
for_each_mayday_cpu(cpu, wq->mayday_mask) {
unsigned int tcpu = is_unbound ? WORK_CPU_UNBOUND : cpu;
struct cpu_workqueue_struct *cwq = get_cwq(tcpu, wq);
struct global_cwq *gcwq = cwq->gcwq;
struct work_struct *work, *n;
__set_current_state(TASK_RUNNING);
mayday_clear_cpu(cpu, wq->mayday_mask);
/* migrate to the target cpu if possible */
rescuer->gcwq = gcwq;
worker_maybe_bind_and_lock(rescuer);
/*
* Slurp in all works issued via this workqueue and
* process'em.
*/
BUG_ON(!list_empty(&rescuer->scheduled));
list_for_each_entry_safe(work, n, &gcwq->worklist, entry)
if (get_work_cwq(work) == cwq)
move_linked_works(work, scheduled, &n);
process_scheduled_works(rescuer);
/*
* Leave this gcwq. If keep_working() is %true, notify a
* regular worker; otherwise, we end up with 0 concurrency
* and stalling the execution.
*/
if (keep_working(gcwq))
wake_up_worker(gcwq);
spin_unlock_irq(&gcwq->lock);
}
schedule();
goto repeat;
}
struct wq_barrier {
struct work_struct work;
struct completion done;
};
static void wq_barrier_func(struct work_struct *work)
{
struct wq_barrier *barr = container_of(work, struct wq_barrier, work);
complete(&barr->done);
}
/**
* insert_wq_barrier - insert a barrier work
* @cwq: cwq to insert barrier into
* @barr: wq_barrier to insert
* @target: target work to attach @barr to
* @worker: worker currently executing @target, NULL if @target is not executing
*
* @barr is linked to @target such that @barr is completed only after
* @target finishes execution. Please note that the ordering
* guarantee is observed only with respect to @target and on the local
* cpu.
*
* Currently, a queued barrier can't be canceled. This is because
* try_to_grab_pending() can't determine whether the work to be
* grabbed is at the head of the queue and thus can't clear LINKED
* flag of the previous work while there must be a valid next work
* after a work with LINKED flag set.
*
* Note that when @worker is non-NULL, @target may be modified
* underneath us, so we can't reliably determine cwq from @target.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock).
*/
static void insert_wq_barrier(struct cpu_workqueue_struct *cwq,
struct wq_barrier *barr,
struct work_struct *target, struct worker *worker)
{
struct list_head *head;
unsigned int linked = 0;
/*
* debugobject calls are safe here even with gcwq->lock locked
* as we know for sure that this will not trigger any of the
* checks and call back into the fixup functions where we
* might deadlock.
*/
INIT_WORK_ONSTACK(&barr->work, wq_barrier_func);
__set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(&barr->work));
init_completion(&barr->done);
/*
* If @target is currently being executed, schedule the
* barrier to the worker; otherwise, put it after @target.
*/
if (worker)
head = worker->scheduled.next;
else {
unsigned long *bits = work_data_bits(target);
head = target->entry.next;
/* there can already be other linked works, inherit and set */
linked = *bits & WORK_STRUCT_LINKED;
__set_bit(WORK_STRUCT_LINKED_BIT, bits);
}
debug_work_activate(&barr->work);
insert_work(cwq, &barr->work, head,
work_color_to_flags(WORK_NO_COLOR) | linked);
}
/**
* flush_workqueue_prep_cwqs - prepare cwqs for workqueue flushing
* @wq: workqueue being flushed
* @flush_color: new flush color, < 0 for no-op
* @work_color: new work color, < 0 for no-op
*
* Prepare cwqs for workqueue flushing.
*
* If @flush_color is non-negative, flush_color on all cwqs should be
* -1. If no cwq has in-flight commands at the specified color, all
* cwq->flush_color's stay at -1 and %false is returned. If any cwq
* has in flight commands, its cwq->flush_color is set to
* @flush_color, @wq->nr_cwqs_to_flush is updated accordingly, cwq
* wakeup logic is armed and %true is returned.
*
* The caller should have initialized @wq->first_flusher prior to
* calling this function with non-negative @flush_color. If
* @flush_color is negative, no flush color update is done and %false
* is returned.
*
* If @work_color is non-negative, all cwqs should have the same
* work_color which is previous to @work_color and all will be
* advanced to @work_color.
*
* CONTEXT:
* mutex_lock(wq->flush_mutex).
*
* RETURNS:
* %true if @flush_color >= 0 and there's something to flush. %false
* otherwise.
*/
static bool flush_workqueue_prep_cwqs(struct workqueue_struct *wq,
int flush_color, int work_color)
{
bool wait = false;
unsigned int cpu;
if (flush_color >= 0) {
BUG_ON(atomic_read(&wq->nr_cwqs_to_flush));
atomic_set(&wq->nr_cwqs_to_flush, 1);
}
for_each_cwq_cpu(cpu, wq) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
struct global_cwq *gcwq = cwq->gcwq;
spin_lock_irq(&gcwq->lock);
if (flush_color >= 0) {
BUG_ON(cwq->flush_color != -1);
if (cwq->nr_in_flight[flush_color]) {
cwq->flush_color = flush_color;
atomic_inc(&wq->nr_cwqs_to_flush);
wait = true;
}
}
if (work_color >= 0) {
BUG_ON(work_color != work_next_color(cwq->work_color));
cwq->work_color = work_color;
}
spin_unlock_irq(&gcwq->lock);
}
if (flush_color >= 0 && atomic_dec_and_test(&wq->nr_cwqs_to_flush))
complete(&wq->first_flusher->done);
return wait;
}
/**
* flush_workqueue - ensure that any scheduled work has run to completion.
* @wq: workqueue to flush
*
* Forces execution of the workqueue and blocks until its completion.
* This is typically used in driver shutdown handlers.
*
* We sleep until all works which were queued on entry have been handled,
* but we are not livelocked by new incoming ones.
*/
void flush_workqueue(struct workqueue_struct *wq)
{
struct wq_flusher this_flusher = {
.list = LIST_HEAD_INIT(this_flusher.list),
.flush_color = -1,
.done = COMPLETION_INITIALIZER_ONSTACK(this_flusher.done),
};
int next_color;
lock_map_acquire(&wq->lockdep_map);
lock_map_release(&wq->lockdep_map);
mutex_lock(&wq->flush_mutex);
/*
* Start-to-wait phase
*/
next_color = work_next_color(wq->work_color);
if (next_color != wq->flush_color) {
/*
* Color space is not full. The current work_color
* becomes our flush_color and work_color is advanced
* by one.
*/
BUG_ON(!list_empty(&wq->flusher_overflow));
this_flusher.flush_color = wq->work_color;
wq->work_color = next_color;
if (!wq->first_flusher) {
/* no flush in progress, become the first flusher */
BUG_ON(wq->flush_color != this_flusher.flush_color);
wq->first_flusher = &this_flusher;
if (!flush_workqueue_prep_cwqs(wq, wq->flush_color,
wq->work_color)) {
/* nothing to flush, done */
wq->flush_color = next_color;
wq->first_flusher = NULL;
goto out_unlock;
}
} else {
/* wait in queue */
BUG_ON(wq->flush_color == this_flusher.flush_color);
list_add_tail(&this_flusher.list, &wq->flusher_queue);
flush_workqueue_prep_cwqs(wq, -1, wq->work_color);
}
} else {
/*
* Oops, color space is full, wait on overflow queue.
* The next flush completion will assign us
* flush_color and transfer to flusher_queue.
*/
list_add_tail(&this_flusher.list, &wq->flusher_overflow);
}
mutex_unlock(&wq->flush_mutex);
wait_for_completion(&this_flusher.done);
/*
* Wake-up-and-cascade phase
*
* First flushers are responsible for cascading flushes and
* handling overflow. Non-first flushers can simply return.
*/
if (wq->first_flusher != &this_flusher)
return;
mutex_lock(&wq->flush_mutex);
/* we might have raced, check again with mutex held */
if (wq->first_flusher != &this_flusher)
goto out_unlock;
wq->first_flusher = NULL;
BUG_ON(!list_empty(&this_flusher.list));
BUG_ON(wq->flush_color != this_flusher.flush_color);
while (true) {
struct wq_flusher *next, *tmp;
/* complete all the flushers sharing the current flush color */
list_for_each_entry_safe(next, tmp, &wq->flusher_queue, list) {
if (next->flush_color != wq->flush_color)
break;
list_del_init(&next->list);
complete(&next->done);
}
BUG_ON(!list_empty(&wq->flusher_overflow) &&
wq->flush_color != work_next_color(wq->work_color));
/* this flush_color is finished, advance by one */
wq->flush_color = work_next_color(wq->flush_color);
/* one color has been freed, handle overflow queue */
if (!list_empty(&wq->flusher_overflow)) {
/*
* Assign the same color to all overflowed
* flushers, advance work_color and append to
* flusher_queue. This is the start-to-wait
* phase for these overflowed flushers.
*/
list_for_each_entry(tmp, &wq->flusher_overflow, list)
tmp->flush_color = wq->work_color;
wq->work_color = work_next_color(wq->work_color);
list_splice_tail_init(&wq->flusher_overflow,
&wq->flusher_queue);
flush_workqueue_prep_cwqs(wq, -1, wq->work_color);
}
if (list_empty(&wq->flusher_queue)) {
BUG_ON(wq->flush_color != wq->work_color);
break;
}
/*
* Need to flush more colors. Make the next flusher
* the new first flusher and arm cwqs.
*/
BUG_ON(wq->flush_color == wq->work_color);
BUG_ON(wq->flush_color != next->flush_color);
list_del_init(&next->list);
wq->first_flusher = next;
if (flush_workqueue_prep_cwqs(wq, wq->flush_color, -1))
break;
/*
* Meh... this color is already done, clear first
* flusher and repeat cascading.
*/
wq->first_flusher = NULL;
}
out_unlock:
mutex_unlock(&wq->flush_mutex);
}
EXPORT_SYMBOL_GPL(flush_workqueue);
/**
* drain_workqueue - drain a workqueue
* @wq: workqueue to drain
*
* Wait until the workqueue becomes empty. While draining is in progress,
* only chain queueing is allowed. IOW, only currently pending or running
* work items on @wq can queue further work items on it. @wq is flushed
* repeatedly until it becomes empty. The number of flushing is detemined
* by the depth of chaining and should be relatively short. Whine if it
* takes too long.
*/
void drain_workqueue(struct workqueue_struct *wq)
{
unsigned int flush_cnt = 0;
unsigned int cpu;
/*
* __queue_work() needs to test whether there are drainers, is much
* hotter than drain_workqueue() and already looks at @wq->flags.
* Use WQ_DRAINING so that queue doesn't have to check nr_drainers.
*/
spin_lock(&workqueue_lock);
if (!wq->nr_drainers++)
wq->flags |= WQ_DRAINING;
spin_unlock(&workqueue_lock);
reflush:
flush_workqueue(wq);
for_each_cwq_cpu(cpu, wq) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
bool drained;
spin_lock_irq(&cwq->gcwq->lock);
drained = !cwq->nr_active && list_empty(&cwq->delayed_works);
spin_unlock_irq(&cwq->gcwq->lock);
if (drained)
continue;
if (++flush_cnt == 10 ||
(flush_cnt % 100 == 0 && flush_cnt <= 1000))
pr_warning("workqueue %s: flush on destruction isn't complete after %u tries\n",
wq->name, flush_cnt);
goto reflush;
}
spin_lock(&workqueue_lock);
if (!--wq->nr_drainers)
wq->flags &= ~WQ_DRAINING;
spin_unlock(&workqueue_lock);
}
EXPORT_SYMBOL_GPL(drain_workqueue);
static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
bool wait_executing)
{
struct worker *worker = NULL;
struct global_cwq *gcwq;
struct cpu_workqueue_struct *cwq;
might_sleep();
gcwq = get_work_gcwq(work);
if (!gcwq)
return false;
spin_lock_irq(&gcwq->lock);
if (!list_empty(&work->entry)) {
/*
* See the comment near try_to_grab_pending()->smp_rmb().
* If it was re-queued to a different gcwq under us, we
* are not going to wait.
*/
smp_rmb();
cwq = get_work_cwq(work);
if (unlikely(!cwq || gcwq != cwq->gcwq))
goto already_gone;
} else if (wait_executing) {
worker = find_worker_executing_work(gcwq, work);
if (!worker)
goto already_gone;
cwq = worker->current_cwq;
} else
goto already_gone;
insert_wq_barrier(cwq, barr, work, worker);
spin_unlock_irq(&gcwq->lock);
/*
* If @max_active is 1 or rescuer is in use, flushing another work
* item on the same workqueue may lead to deadlock. Make sure the
* flusher is not running on the same workqueue by verifying write
* access.
*/
if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER)
lock_map_acquire(&cwq->wq->lockdep_map);
else
lock_map_acquire_read(&cwq->wq->lockdep_map);
lock_map_release(&cwq->wq->lockdep_map);
return true;
already_gone:
spin_unlock_irq(&gcwq->lock);
return false;
}
/**
* flush_work - wait for a work to finish executing the last queueing instance
* @work: the work to flush
*
* Wait until @work has finished execution. This function considers
* only the last queueing instance of @work. If @work has been
* enqueued across different CPUs on a non-reentrant workqueue or on
* multiple workqueues, @work might still be executing on return on
* some of the CPUs from earlier queueing.
*
* If @work was queued only on a non-reentrant, ordered or unbound
* workqueue, @work is guaranteed to be idle on return if it hasn't
* been requeued since flush started.
*
* RETURNS:
* %true if flush_work() waited for the work to finish execution,
* %false if it was already idle.
*/
bool flush_work(struct work_struct *work)
{
struct wq_barrier barr;
if (start_flush_work(work, &barr, true)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
return true;
} else
return false;
}
EXPORT_SYMBOL_GPL(flush_work);
static bool wait_on_cpu_work(struct global_cwq *gcwq, struct work_struct *work)
{
struct wq_barrier barr;
struct worker *worker;
spin_lock_irq(&gcwq->lock);
worker = find_worker_executing_work(gcwq, work);
if (unlikely(worker))
insert_wq_barrier(worker->current_cwq, &barr, work, worker);
spin_unlock_irq(&gcwq->lock);
if (unlikely(worker)) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
return true;
} else
return false;
}
static bool wait_on_work(struct work_struct *work)
{
bool ret = false;
int cpu;
might_sleep();
lock_map_acquire(&work->lockdep_map);
lock_map_release(&work->lockdep_map);
for_each_gcwq_cpu(cpu)
ret |= wait_on_cpu_work(get_gcwq(cpu), work);
return ret;
}
/**
* flush_work_sync - wait until a work has finished execution
* @work: the work to flush
*
* Wait until @work has finished execution. On return, it's
* guaranteed that all queueing instances of @work which happened
* before this function is called are finished. In other words, if
* @work hasn't been requeued since this function was called, @work is
* guaranteed to be idle on return.
*
* RETURNS:
* %true if flush_work_sync() waited for the work to finish execution,
* %false if it was already idle.
*/
bool flush_work_sync(struct work_struct *work)
{
struct wq_barrier barr;
bool pending, waited;
/* we'll wait for executions separately, queue barr only if pending */
pending = start_flush_work(work, &barr, false);
/* wait for executions to finish */
waited = wait_on_work(work);
/* wait for the pending one */
if (pending) {
wait_for_completion(&barr.done);
destroy_work_on_stack(&barr.work);
}
return pending || waited;
}
EXPORT_SYMBOL_GPL(flush_work_sync);
/*
* Upon a successful return (>= 0), the caller "owns" WORK_STRUCT_PENDING bit,
* so this work can't be re-armed in any way.
*/
static int try_to_grab_pending(struct work_struct *work)
{
struct global_cwq *gcwq;
int ret = -1;
if (!test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(work)))
return 0;
/*
* The queueing is in progress, or it is already queued. Try to
* steal it from ->worklist without clearing WORK_STRUCT_PENDING.
*/
gcwq = get_work_gcwq(work);
if (!gcwq)
return ret;
spin_lock_irq(&gcwq->lock);
if (!list_empty(&work->entry)) {
/*
* This work is queued, but perhaps we locked the wrong gcwq.
* In that case we must see the new value after rmb(), see
* insert_work()->wmb().
*/
smp_rmb();
if (gcwq == get_work_gcwq(work)) {
debug_work_deactivate(work);
list_del_init(&work->entry);
cwq_dec_nr_in_flight(get_work_cwq(work),
get_work_color(work),
*work_data_bits(work) & WORK_STRUCT_DELAYED);
ret = 1;
}
}
spin_unlock_irq(&gcwq->lock);
return ret;
}
static bool __cancel_work_timer(struct work_struct *work,
struct timer_list* timer)
{
int ret;
do {
ret = (timer && likely(del_timer(timer)));
if (!ret)
ret = try_to_grab_pending(work);
wait_on_work(work);
} while (unlikely(ret < 0));
clear_work_data(work);
return ret;
}
/**
* cancel_work_sync - cancel a work and wait for it to finish
* @work: the work to cancel
*
* Cancel @work and wait for its execution to finish. This function
* can be used even if the work re-queues itself or migrates to
* another workqueue. On return from this function, @work is
* guaranteed to be not pending or executing on any CPU.
*
* cancel_work_sync(&delayed_work->work) must not be used for
* delayed_work's. Use cancel_delayed_work_sync() instead.
*
* The caller must ensure that the workqueue on which @work was last
* queued can't be destroyed before this function returns.
*
* RETURNS:
* %true if @work was pending, %false otherwise.
*/
bool cancel_work_sync(struct work_struct *work)
{
return __cancel_work_timer(work, NULL);
}
EXPORT_SYMBOL_GPL(cancel_work_sync);
/**
* flush_delayed_work - wait for a dwork to finish executing the last queueing
* @dwork: the delayed work to flush
*
* Delayed timer is cancelled and the pending work is queued for
* immediate execution. Like flush_work(), this function only
* considers the last queueing instance of @dwork.
*
* RETURNS:
* %true if flush_work() waited for the work to finish execution,
* %false if it was already idle.
*/
bool flush_delayed_work(struct delayed_work *dwork)
{
if (del_timer_sync(&dwork->timer))
__queue_work(raw_smp_processor_id(),
get_work_cwq(&dwork->work)->wq, &dwork->work);
return flush_work(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work);
/**
* flush_delayed_work_sync - wait for a dwork to finish
* @dwork: the delayed work to flush
*
* Delayed timer is cancelled and the pending work is queued for
* execution immediately. Other than timer handling, its behavior
* is identical to flush_work_sync().
*
* RETURNS:
* %true if flush_work_sync() waited for the work to finish execution,
* %false if it was already idle.
*/
bool flush_delayed_work_sync(struct delayed_work *dwork)
{
if (del_timer_sync(&dwork->timer))
__queue_work(raw_smp_processor_id(),
get_work_cwq(&dwork->work)->wq, &dwork->work);
return flush_work_sync(&dwork->work);
}
EXPORT_SYMBOL(flush_delayed_work_sync);
/**
* cancel_delayed_work_sync - cancel a delayed work and wait for it to finish
* @dwork: the delayed work cancel
*
* This is cancel_work_sync() for delayed works.
*
* RETURNS:
* %true if @dwork was pending, %false otherwise.
*/
bool cancel_delayed_work_sync(struct delayed_work *dwork)
{
return __cancel_work_timer(&dwork->work, &dwork->timer);
}
EXPORT_SYMBOL(cancel_delayed_work_sync);
/**
* schedule_work - put work task in global workqueue
* @work: job to be done
*
* Returns zero if @work was already on the kernel-global workqueue and
* non-zero otherwise.
*
* This puts a job in the kernel-global workqueue if it was not already
* queued and leaves it in the same position on the kernel-global
* workqueue otherwise.
*/
int schedule_work(struct work_struct *work)
{
return queue_work(system_wq, work);
}
EXPORT_SYMBOL(schedule_work);
/*
* schedule_work_on - put work task on a specific cpu
* @cpu: cpu to put the work task on
* @work: job to be done
*
* This puts a job on a specific cpu
*/
int schedule_work_on(int cpu, struct work_struct *work)
{
return queue_work_on(cpu, system_wq, work);
}
EXPORT_SYMBOL(schedule_work_on);
/**
* schedule_delayed_work - put work task in global workqueue after delay
* @dwork: job to be done
* @delay: number of jiffies to wait or 0 for immediate execution
*
* After waiting for a given time this puts a job in the kernel-global
* workqueue.
*/
int schedule_delayed_work(struct delayed_work *dwork,
unsigned long delay)
{
return queue_delayed_work(system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work);
/**
* schedule_delayed_work_on - queue work in global workqueue on CPU after delay
* @cpu: cpu to use
* @dwork: job to be done
* @delay: number of jiffies to wait
*
* After waiting for a given time this puts a job in the kernel-global
* workqueue on the specified CPU.
*/
int schedule_delayed_work_on(int cpu,
struct delayed_work *dwork, unsigned long delay)
{
return queue_delayed_work_on(cpu, system_wq, dwork, delay);
}
EXPORT_SYMBOL(schedule_delayed_work_on);
/**
* schedule_on_each_cpu - execute a function synchronously on each online CPU
* @func: the function to call
*
* schedule_on_each_cpu() executes @func on each online CPU using the
* system workqueue and blocks until all CPUs have completed.
* schedule_on_each_cpu() is very slow.
*
* RETURNS:
* 0 on success, -errno on failure.
*/
int schedule_on_each_cpu(work_func_t func)
{
int cpu;
struct work_struct __percpu *works;
works = alloc_percpu(struct work_struct);
if (!works)
return -ENOMEM;
get_online_cpus();
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);
INIT_WORK(work, func);
schedule_work_on(cpu, work);
}
for_each_online_cpu(cpu)
flush_work(per_cpu_ptr(works, cpu));
put_online_cpus();
free_percpu(works);
return 0;
}
/**
* flush_scheduled_work - ensure that any scheduled work has run to completion.
*
* Forces execution of the kernel-global workqueue and blocks until its
* completion.
*
* Think twice before calling this function! It's very easy to get into
* trouble if you don't take great care. Either of the following situations
* will lead to deadlock:
*
* One of the work items currently on the workqueue needs to acquire
* a lock held by your code or its caller.
*
* Your code is running in the context of a work routine.
*
* They will be detected by lockdep when they occur, but the first might not
* occur very often. It depends on what work items are on the workqueue and
* what locks they need, which you have no control over.
*
* In most situations flushing the entire workqueue is overkill; you merely
* need to know that a particular work item isn't queued and isn't running.
* In such cases you should use cancel_delayed_work_sync() or
* cancel_work_sync() instead.
*/
void flush_scheduled_work(void)
{
flush_workqueue(system_wq);
}
EXPORT_SYMBOL(flush_scheduled_work);
/**
* execute_in_process_context - reliably execute the routine with user context
* @fn: the function to execute
* @ew: guaranteed storage for the execute work structure (must
* be available when the work executes)
*
* Executes the function immediately if process context is available,
* otherwise schedules the function for delayed execution.
*
* Returns: 0 - function was executed
* 1 - function was scheduled for execution
*/
int execute_in_process_context(work_func_t fn, struct execute_work *ew)
{
if (!in_interrupt()) {
fn(&ew->work);
return 0;
}
INIT_WORK(&ew->work, fn);
schedule_work(&ew->work);
return 1;
}
EXPORT_SYMBOL_GPL(execute_in_process_context);
int keventd_up(void)
{
return system_wq != NULL;
}
static int alloc_cwqs(struct workqueue_struct *wq)
{
/*
* cwqs are forced aligned according to WORK_STRUCT_FLAG_BITS.
* Make sure that the alignment isn't lower than that of
* unsigned long long.
*/
const size_t size = sizeof(struct cpu_workqueue_struct);
const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
__alignof__(unsigned long long));
#ifdef CONFIG_SMP
bool percpu = !(wq->flags & WQ_UNBOUND);
#else
bool percpu = false;
#endif
if (percpu)
wq->cpu_wq.pcpu = __alloc_percpu(size, align);
else {
void *ptr;
/*
* Allocate enough room to align cwq and put an extra
* pointer at the end pointing back to the originally
* allocated pointer which will be used for free.
*/
ptr = kzalloc(size + align + sizeof(void *), GFP_KERNEL);
if (ptr) {
wq->cpu_wq.single = PTR_ALIGN(ptr, align);
*(void **)(wq->cpu_wq.single + 1) = ptr;
}
}
/* just in case, make sure it's actually aligned */
BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
return wq->cpu_wq.v ? 0 : -ENOMEM;
}
static void free_cwqs(struct workqueue_struct *wq)
{
#ifdef CONFIG_SMP
bool percpu = !(wq->flags & WQ_UNBOUND);
#else
bool percpu = false;
#endif
if (percpu)
free_percpu(wq->cpu_wq.pcpu);
else if (wq->cpu_wq.single) {
/* the pointer to free is stored right after the cwq */
kfree(*(void **)(wq->cpu_wq.single + 1));
}
}
static int wq_clamp_max_active(int max_active, unsigned int flags,
const char *name)
{
int lim = flags & WQ_UNBOUND ? WQ_UNBOUND_MAX_ACTIVE : WQ_MAX_ACTIVE;
if (max_active < 1 || max_active > lim)
printk(KERN_WARNING "workqueue: max_active %d requested for %s "
"is out of range, clamping between %d and %d\n",
max_active, name, 1, lim);
return clamp_val(max_active, 1, lim);
}
struct workqueue_struct *__alloc_workqueue_key(const char *name,
unsigned int flags,
int max_active,
struct lock_class_key *key,
const char *lock_name)
{
struct workqueue_struct *wq;
unsigned int cpu;
/*
* Workqueues which may be used during memory reclaim should
* have a rescuer to guarantee forward progress.
*/
if (flags & WQ_MEM_RECLAIM)
flags |= WQ_RESCUER;
/*
* Unbound workqueues aren't concurrency managed and should be
* dispatched to workers immediately.
*/
if (flags & WQ_UNBOUND)
flags |= WQ_HIGHPRI;
max_active = max_active ?: WQ_DFL_ACTIVE;
max_active = wq_clamp_max_active(max_active, flags, name);
wq = kzalloc(sizeof(*wq), GFP_KERNEL);
if (!wq)
goto err;
wq->flags = flags;
wq->saved_max_active = max_active;
mutex_init(&wq->flush_mutex);
atomic_set(&wq->nr_cwqs_to_flush, 0);
INIT_LIST_HEAD(&wq->flusher_queue);
INIT_LIST_HEAD(&wq->flusher_overflow);
wq->name = name;
lockdep_init_map(&wq->lockdep_map, lock_name, key, 0);
INIT_LIST_HEAD(&wq->list);
if (alloc_cwqs(wq) < 0)
goto err;
for_each_cwq_cpu(cpu, wq) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
struct global_cwq *gcwq = get_gcwq(cpu);
BUG_ON((unsigned long)cwq & WORK_STRUCT_FLAG_MASK);
cwq->gcwq = gcwq;
cwq->wq = wq;
cwq->flush_color = -1;
cwq->max_active = max_active;
INIT_LIST_HEAD(&cwq->delayed_works);
}
if (flags & WQ_RESCUER) {
struct worker *rescuer;
if (!alloc_mayday_mask(&wq->mayday_mask, GFP_KERNEL))
goto err;
wq->rescuer = rescuer = alloc_worker();
if (!rescuer)
goto err;
rescuer->task = kthread_create(rescuer_thread, wq, "%s", name);
if (IS_ERR(rescuer->task))
goto err;
rescuer->task->flags |= PF_THREAD_BOUND;
wake_up_process(rescuer->task);
}
/*
* workqueue_lock protects global freeze state and workqueues
* list. Grab it, set max_active accordingly and add the new
* workqueue to workqueues list.
*/
spin_lock(&workqueue_lock);
if (workqueue_freezing && wq->flags & WQ_FREEZABLE)
for_each_cwq_cpu(cpu, wq)
get_cwq(cpu, wq)->max_active = 0;
list_add(&wq->list, &workqueues);
spin_unlock(&workqueue_lock);
return wq;
err:
if (wq) {
free_cwqs(wq);
free_mayday_mask(wq->mayday_mask);
kfree(wq->rescuer);
kfree(wq);
}
return NULL;
}
EXPORT_SYMBOL_GPL(__alloc_workqueue_key);
/**
* destroy_workqueue - safely terminate a workqueue
* @wq: target workqueue
*
* Safely destroy a workqueue. All work currently pending will be done first.
*/
void destroy_workqueue(struct workqueue_struct *wq)
{
unsigned int cpu;
/* drain it before proceeding with destruction */
drain_workqueue(wq);
/*
* wq list is used to freeze wq, remove from list after
* flushing is complete in case freeze races us.
*/
spin_lock(&workqueue_lock);
list_del(&wq->list);
spin_unlock(&workqueue_lock);
/* sanity check */
for_each_cwq_cpu(cpu, wq) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
int i;
for (i = 0; i < WORK_NR_COLORS; i++)
BUG_ON(cwq->nr_in_flight[i]);
BUG_ON(cwq->nr_active);
BUG_ON(!list_empty(&cwq->delayed_works));
}
if (wq->flags & WQ_RESCUER) {
kthread_stop(wq->rescuer->task);
free_mayday_mask(wq->mayday_mask);
kfree(wq->rescuer);
}
free_cwqs(wq);
kfree(wq);
}
EXPORT_SYMBOL_GPL(destroy_workqueue);
/**
* workqueue_set_max_active - adjust max_active of a workqueue
* @wq: target workqueue
* @max_active: new max_active value.
*
* Set max_active of @wq to @max_active.
*
* CONTEXT:
* Don't call from IRQ context.
*/
void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
{
unsigned int cpu;
max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
spin_lock(&workqueue_lock);
wq->saved_max_active = max_active;
for_each_cwq_cpu(cpu, wq) {
struct global_cwq *gcwq = get_gcwq(cpu);
spin_lock_irq(&gcwq->lock);
if (!(wq->flags & WQ_FREEZABLE) ||
!(gcwq->flags & GCWQ_FREEZING))
get_cwq(gcwq->cpu, wq)->max_active = max_active;
spin_unlock_irq(&gcwq->lock);
}
spin_unlock(&workqueue_lock);
}
EXPORT_SYMBOL_GPL(workqueue_set_max_active);
/**
* workqueue_congested - test whether a workqueue is congested
* @cpu: CPU in question
* @wq: target workqueue
*
* Test whether @wq's cpu workqueue for @cpu is congested. There is
* no synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
*
* RETURNS:
* %true if congested, %false otherwise.
*/
bool workqueue_congested(unsigned int cpu, struct workqueue_struct *wq)
{
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
return !list_empty(&cwq->delayed_works);
}
EXPORT_SYMBOL_GPL(workqueue_congested);
/**
* work_cpu - return the last known associated cpu for @work
* @work: the work of interest
*
* RETURNS:
* CPU number if @work was ever queued. WORK_CPU_NONE otherwise.
*/
unsigned int work_cpu(struct work_struct *work)
{
struct global_cwq *gcwq = get_work_gcwq(work);
return gcwq ? gcwq->cpu : WORK_CPU_NONE;
}
EXPORT_SYMBOL_GPL(work_cpu);
/**
* work_busy - test whether a work is currently pending or running
* @work: the work to be tested
*
* Test whether @work is currently pending or running. There is no
* synchronization around this function and the test result is
* unreliable and only useful as advisory hints or for debugging.
* Especially for reentrant wqs, the pending state might hide the
* running state.
*
* RETURNS:
* OR'd bitmask of WORK_BUSY_* bits.
*/
unsigned int work_busy(struct work_struct *work)
{
struct global_cwq *gcwq = get_work_gcwq(work);
unsigned long flags;
unsigned int ret = 0;
if (!gcwq)
return false;
spin_lock_irqsave(&gcwq->lock, flags);
if (work_pending(work))
ret |= WORK_BUSY_PENDING;
if (find_worker_executing_work(gcwq, work))
ret |= WORK_BUSY_RUNNING;
spin_unlock_irqrestore(&gcwq->lock, flags);
return ret;
}
EXPORT_SYMBOL_GPL(work_busy);
/*
* CPU hotplug.
*
* There are two challenges in supporting CPU hotplug. Firstly, there
* are a lot of assumptions on strong associations among work, cwq and
* gcwq which make migrating pending and scheduled works very
* difficult to implement without impacting hot paths. Secondly,
* gcwqs serve mix of short, long and very long running works making
* blocked draining impractical.
*
* This is solved by allowing a gcwq to be detached from CPU, running
* it with unbound (rogue) workers and allowing it to be reattached
* later if the cpu comes back online. A separate thread is created
* to govern a gcwq in such state and is called the trustee of the
* gcwq.
*
* Trustee states and their descriptions.
*
* START Command state used on startup. On CPU_DOWN_PREPARE, a
* new trustee is started with this state.
*
* IN_CHARGE Once started, trustee will enter this state after
* assuming the manager role and making all existing
* workers rogue. DOWN_PREPARE waits for trustee to
* enter this state. After reaching IN_CHARGE, trustee
* tries to execute the pending worklist until it's empty
* and the state is set to BUTCHER, or the state is set
* to RELEASE.
*
* BUTCHER Command state which is set by the cpu callback after
* the cpu has went down. Once this state is set trustee
* knows that there will be no new works on the worklist
* and once the worklist is empty it can proceed to
* killing idle workers.
*
* RELEASE Command state which is set by the cpu callback if the
* cpu down has been canceled or it has come online
* again. After recognizing this state, trustee stops
* trying to drain or butcher and clears ROGUE, rebinds
* all remaining workers back to the cpu and releases
* manager role.
*
* DONE Trustee will enter this state after BUTCHER or RELEASE
* is complete.
*
* trustee CPU draining
* took over down complete
* START -----------> IN_CHARGE -----------> BUTCHER -----------> DONE
* | | ^
* | CPU is back online v return workers |
* ----------------> RELEASE --------------
*/
/**
* trustee_wait_event_timeout - timed event wait for trustee
* @cond: condition to wait for
* @timeout: timeout in jiffies
*
* wait_event_timeout() for trustee to use. Handles locking and
* checks for RELEASE request.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. To be used by trustee.
*
* RETURNS:
* Positive indicating left time if @cond is satisfied, 0 if timed
* out, -1 if canceled.
*/
#define trustee_wait_event_timeout(cond, timeout) ({ \
long __ret = (timeout); \
while (!((cond) || (gcwq->trustee_state == TRUSTEE_RELEASE)) && \
__ret) { \
spin_unlock_irq(&gcwq->lock); \
__wait_event_timeout(gcwq->trustee_wait, (cond) || \
(gcwq->trustee_state == TRUSTEE_RELEASE), \
__ret); \
spin_lock_irq(&gcwq->lock); \
} \
gcwq->trustee_state == TRUSTEE_RELEASE ? -1 : (__ret); \
})
/**
* trustee_wait_event - event wait for trustee
* @cond: condition to wait for
*
* wait_event() for trustee to use. Automatically handles locking and
* checks for CANCEL request.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. To be used by trustee.
*
* RETURNS:
* 0 if @cond is satisfied, -1 if canceled.
*/
#define trustee_wait_event(cond) ({ \
long __ret1; \
__ret1 = trustee_wait_event_timeout(cond, MAX_SCHEDULE_TIMEOUT);\
__ret1 < 0 ? -1 : 0; \
})
static int __cpuinit trustee_thread(void *__gcwq)
{
struct global_cwq *gcwq = __gcwq;
struct worker *worker;
struct work_struct *work;
struct hlist_node *pos;
long rc;
int i;
BUG_ON(gcwq->cpu != smp_processor_id());
spin_lock_irq(&gcwq->lock);
/*
* Claim the manager position and make all workers rogue.
* Trustee must be bound to the target cpu and can't be
* cancelled.
*/
BUG_ON(gcwq->cpu != smp_processor_id());
rc = trustee_wait_event(!(gcwq->flags & GCWQ_MANAGING_WORKERS));
BUG_ON(rc < 0);
gcwq->flags |= GCWQ_MANAGING_WORKERS;
list_for_each_entry(worker, &gcwq->idle_list, entry)
worker->flags |= WORKER_ROGUE;
for_each_busy_worker(worker, i, pos, gcwq)
worker->flags |= WORKER_ROGUE;
/*
* Call schedule() so that we cross rq->lock and thus can
* guarantee sched callbacks see the rogue flag. This is
* necessary as scheduler callbacks may be invoked from other
* cpus.
*/
spin_unlock_irq(&gcwq->lock);
schedule();
spin_lock_irq(&gcwq->lock);
/*
* Sched callbacks are disabled now. Zap nr_running. After
* this, nr_running stays zero and need_more_worker() and
* keep_working() are always true as long as the worklist is
* not empty.
*/
atomic_set(get_gcwq_nr_running(gcwq->cpu), 0);
spin_unlock_irq(&gcwq->lock);
del_timer_sync(&gcwq->idle_timer);
spin_lock_irq(&gcwq->lock);
/*
* We're now in charge. Notify and proceed to drain. We need
* to keep the gcwq running during the whole CPU down
* procedure as other cpu hotunplug callbacks may need to
* flush currently running tasks.
*/
gcwq->trustee_state = TRUSTEE_IN_CHARGE;
wake_up_all(&gcwq->trustee_wait);
/*
* The original cpu is in the process of dying and may go away
* anytime now. When that happens, we and all workers would
* be migrated to other cpus. Try draining any left work. We
* want to get it over with ASAP - spam rescuers, wake up as
* many idlers as necessary and create new ones till the
* worklist is empty. Note that if the gcwq is frozen, there
* may be frozen works in freezable cwqs. Don't declare
* completion while frozen.
*/
while (gcwq->nr_workers != gcwq->nr_idle ||
gcwq->flags & GCWQ_FREEZING ||
gcwq->trustee_state == TRUSTEE_IN_CHARGE) {
int nr_works = 0;
list_for_each_entry(work, &gcwq->worklist, entry) {
send_mayday(work);
nr_works++;
}
list_for_each_entry(worker, &gcwq->idle_list, entry) {
if (!nr_works--)
break;
wake_up_process(worker->task);
}
if (need_to_create_worker(gcwq)) {
spin_unlock_irq(&gcwq->lock);
worker = create_worker(gcwq, false);
spin_lock_irq(&gcwq->lock);
if (worker) {
worker->flags |= WORKER_ROGUE;
start_worker(worker);
}
}
/* give a breather */
if (trustee_wait_event_timeout(false, TRUSTEE_COOLDOWN) < 0)
break;
}
/*
* Either all works have been scheduled and cpu is down, or
* cpu down has already been canceled. Wait for and butcher
* all workers till we're canceled.
*/
do {
rc = trustee_wait_event(!list_empty(&gcwq->idle_list));
while (!list_empty(&gcwq->idle_list))
destroy_worker(list_first_entry(&gcwq->idle_list,
struct worker, entry));
} while (gcwq->nr_workers && rc >= 0);
/*
* At this point, either draining has completed and no worker
* is left, or cpu down has been canceled or the cpu is being
* brought back up. There shouldn't be any idle one left.
* Tell the remaining busy ones to rebind once it finishes the
* currently scheduled works by scheduling the rebind_work.
*/
WARN_ON(!list_empty(&gcwq->idle_list));
for_each_busy_worker(worker, i, pos, gcwq) {
struct work_struct *rebind_work = &worker->rebind_work;
/*
* Rebind_work may race with future cpu hotplug
* operations. Use a separate flag to mark that
* rebinding is scheduled.
*/
worker->flags |= WORKER_REBIND;
worker->flags &= ~WORKER_ROGUE;
/* queue rebind_work, wq doesn't matter, use the default one */
if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
work_data_bits(rebind_work)))
continue;
debug_work_activate(rebind_work);
insert_work(get_cwq(gcwq->cpu, system_wq), rebind_work,
worker->scheduled.next,
work_color_to_flags(WORK_NO_COLOR));
}
/* relinquish manager role */
gcwq->flags &= ~GCWQ_MANAGING_WORKERS;
/* notify completion */
gcwq->trustee = NULL;
gcwq->trustee_state = TRUSTEE_DONE;
wake_up_all(&gcwq->trustee_wait);
spin_unlock_irq(&gcwq->lock);
return 0;
}
/**
* wait_trustee_state - wait for trustee to enter the specified state
* @gcwq: gcwq the trustee of interest belongs to
* @state: target state to wait for
*
* Wait for the trustee to reach @state. DONE is already matched.
*
* CONTEXT:
* spin_lock_irq(gcwq->lock) which may be released and regrabbed
* multiple times. To be used by cpu_callback.
*/
static void __cpuinit wait_trustee_state(struct global_cwq *gcwq, int state)
__releases(&gcwq->lock)
__acquires(&gcwq->lock)
{
if (!(gcwq->trustee_state == state ||
gcwq->trustee_state == TRUSTEE_DONE)) {
spin_unlock_irq(&gcwq->lock);
__wait_event(gcwq->trustee_wait,
gcwq->trustee_state == state ||
gcwq->trustee_state == TRUSTEE_DONE);
spin_lock_irq(&gcwq->lock);
}
}
static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
unsigned long action,
void *hcpu)
{
unsigned int cpu = (unsigned long)hcpu;
struct global_cwq *gcwq = get_gcwq(cpu);
struct task_struct *new_trustee = NULL;
struct worker *uninitialized_var(new_worker);
unsigned long flags;
action &= ~CPU_TASKS_FROZEN;
switch (action) {
case CPU_DOWN_PREPARE:
new_trustee = kthread_create(trustee_thread, gcwq,
"workqueue_trustee/%d\n", cpu);
if (IS_ERR(new_trustee))
return notifier_from_errno(PTR_ERR(new_trustee));
kthread_bind(new_trustee, cpu);
/* fall through */
case CPU_UP_PREPARE:
BUG_ON(gcwq->first_idle);
new_worker = create_worker(gcwq, false);
if (!new_worker) {
if (new_trustee)
kthread_stop(new_trustee);
return NOTIFY_BAD;
}
}
/* some are called w/ irq disabled, don't disturb irq status */
spin_lock_irqsave(&gcwq->lock, flags);
switch (action) {
case CPU_DOWN_PREPARE:
/* initialize trustee and tell it to acquire the gcwq */
BUG_ON(gcwq->trustee || gcwq->trustee_state != TRUSTEE_DONE);
gcwq->trustee = new_trustee;
gcwq->trustee_state = TRUSTEE_START;
wake_up_process(gcwq->trustee);
wait_trustee_state(gcwq, TRUSTEE_IN_CHARGE);
/* fall through */
case CPU_UP_PREPARE:
BUG_ON(gcwq->first_idle);
gcwq->first_idle = new_worker;
break;
case CPU_DYING:
/*
* Before this, the trustee and all workers except for
* the ones which are still executing works from
* before the last CPU down must be on the cpu. After
* this, they'll all be diasporas.
*/
gcwq->flags |= GCWQ_DISASSOCIATED;
break;
case CPU_POST_DEAD:
gcwq->trustee_state = TRUSTEE_BUTCHER;
/* fall through */
case CPU_UP_CANCELED:
destroy_worker(gcwq->first_idle);
gcwq->first_idle = NULL;
break;
case CPU_DOWN_FAILED:
case CPU_ONLINE:
gcwq->flags &= ~GCWQ_DISASSOCIATED;
if (gcwq->trustee_state != TRUSTEE_DONE) {
gcwq->trustee_state = TRUSTEE_RELEASE;
wake_up_process(gcwq->trustee);
wait_trustee_state(gcwq, TRUSTEE_DONE);
}
/*
* Trustee is done and there might be no worker left.
* Put the first_idle in and request a real manager to
* take a look.
*/
spin_unlock_irq(&gcwq->lock);
kthread_bind(gcwq->first_idle->task, cpu);
spin_lock_irq(&gcwq->lock);
gcwq->flags |= GCWQ_MANAGE_WORKERS;
start_worker(gcwq->first_idle);
gcwq->first_idle = NULL;
break;
}
spin_unlock_irqrestore(&gcwq->lock, flags);
return notifier_from_errno(0);
}
#ifdef CONFIG_SMP
struct work_for_cpu {
struct completion completion;
long (*fn)(void *);
void *arg;
long ret;
};
static int do_work_for_cpu(void *_wfc)
{
struct work_for_cpu *wfc = _wfc;
wfc->ret = wfc->fn(wfc->arg);
complete(&wfc->completion);
return 0;
}
/**
* work_on_cpu - run a function in user context on a particular cpu
* @cpu: the cpu to run on
* @fn: the function to run
* @arg: the function arg
*
* This will return the value @fn returns.
* It is up to the caller to ensure that the cpu doesn't go offline.
* The caller must not hold any locks which would prevent @fn from completing.
*/
long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg)
{
struct task_struct *sub_thread;
struct work_for_cpu wfc = {
.completion = COMPLETION_INITIALIZER_ONSTACK(wfc.completion),
.fn = fn,
.arg = arg,
};
sub_thread = kthread_create(do_work_for_cpu, &wfc, "work_for_cpu");
if (IS_ERR(sub_thread))
return PTR_ERR(sub_thread);
kthread_bind(sub_thread, cpu);
wake_up_process(sub_thread);
wait_for_completion(&wfc.completion);
return wfc.ret;
}
EXPORT_SYMBOL_GPL(work_on_cpu);
#endif /* CONFIG_SMP */
#ifdef CONFIG_FREEZER
/**
* freeze_workqueues_begin - begin freezing workqueues
*
* Start freezing workqueues. After this function returns, all freezable
* workqueues will queue new works to their frozen_works list instead of
* gcwq->worklist.
*
* CONTEXT:
* Grabs and releases workqueue_lock and gcwq->lock's.
*/
void freeze_workqueues_begin(void)
{
unsigned int cpu;
spin_lock(&workqueue_lock);
BUG_ON(workqueue_freezing);
workqueue_freezing = true;
for_each_gcwq_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct workqueue_struct *wq;
spin_lock_irq(&gcwq->lock);
BUG_ON(gcwq->flags & GCWQ_FREEZING);
gcwq->flags |= GCWQ_FREEZING;
list_for_each_entry(wq, &workqueues, list) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
if (cwq && wq->flags & WQ_FREEZABLE)
cwq->max_active = 0;
}
spin_unlock_irq(&gcwq->lock);
}
spin_unlock(&workqueue_lock);
}
/**
* freeze_workqueues_busy - are freezable workqueues still busy?
*
* Check whether freezing is complete. This function must be called
* between freeze_workqueues_begin() and thaw_workqueues().
*
* CONTEXT:
* Grabs and releases workqueue_lock.
*
* RETURNS:
* %true if some freezable workqueues are still busy. %false if freezing
* is complete.
*/
bool freeze_workqueues_busy(void)
{
unsigned int cpu;
bool busy = false;
spin_lock(&workqueue_lock);
BUG_ON(!workqueue_freezing);
for_each_gcwq_cpu(cpu) {
struct workqueue_struct *wq;
/*
* nr_active is monotonically decreasing. It's safe
* to peek without lock.
*/
list_for_each_entry(wq, &workqueues, list) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
if (!cwq || !(wq->flags & WQ_FREEZABLE))
continue;
BUG_ON(cwq->nr_active < 0);
if (cwq->nr_active) {
busy = true;
goto out_unlock;
}
}
}
out_unlock:
spin_unlock(&workqueue_lock);
return busy;
}
/**
* thaw_workqueues - thaw workqueues
*
* Thaw workqueues. Normal queueing is restored and all collected
* frozen works are transferred to their respective gcwq worklists.
*
* CONTEXT:
* Grabs and releases workqueue_lock and gcwq->lock's.
*/
void thaw_workqueues(void)
{
unsigned int cpu;
spin_lock(&workqueue_lock);
if (!workqueue_freezing)
goto out_unlock;
for_each_gcwq_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct workqueue_struct *wq;
spin_lock_irq(&gcwq->lock);
BUG_ON(!(gcwq->flags & GCWQ_FREEZING));
gcwq->flags &= ~GCWQ_FREEZING;
list_for_each_entry(wq, &workqueues, list) {
struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
if (!cwq || !(wq->flags & WQ_FREEZABLE))
continue;
/* restore max_active and repopulate worklist */
cwq->max_active = wq->saved_max_active;
while (!list_empty(&cwq->delayed_works) &&
cwq->nr_active < cwq->max_active)
cwq_activate_first_delayed(cwq);
}
wake_up_worker(gcwq);
spin_unlock_irq(&gcwq->lock);
}
workqueue_freezing = false;
out_unlock:
spin_unlock(&workqueue_lock);
}
#endif /* CONFIG_FREEZER */
static int __init init_workqueues(void)
{
unsigned int cpu;
int i;
cpu_notifier(workqueue_cpu_callback, CPU_PRI_WORKQUEUE);
/* initialize gcwqs */
for_each_gcwq_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
spin_lock_init(&gcwq->lock);
INIT_LIST_HEAD(&gcwq->worklist);
gcwq->cpu = cpu;
gcwq->flags |= GCWQ_DISASSOCIATED;
INIT_LIST_HEAD(&gcwq->idle_list);
for (i = 0; i < BUSY_WORKER_HASH_SIZE; i++)
INIT_HLIST_HEAD(&gcwq->busy_hash[i]);
init_timer_deferrable(&gcwq->idle_timer);
gcwq->idle_timer.function = idle_worker_timeout;
gcwq->idle_timer.data = (unsigned long)gcwq;
setup_timer(&gcwq->mayday_timer, gcwq_mayday_timeout,
(unsigned long)gcwq);
ida_init(&gcwq->worker_ida);
gcwq->trustee_state = TRUSTEE_DONE;
init_waitqueue_head(&gcwq->trustee_wait);
}
/* create the initial worker */
for_each_online_gcwq_cpu(cpu) {
struct global_cwq *gcwq = get_gcwq(cpu);
struct worker *worker;
if (cpu != WORK_CPU_UNBOUND)
gcwq->flags &= ~GCWQ_DISASSOCIATED;
worker = create_worker(gcwq, true);
BUG_ON(!worker);
spin_lock_irq(&gcwq->lock);
start_worker(worker);
spin_unlock_irq(&gcwq->lock);
}
system_wq = alloc_workqueue("events", 0, 0);
system_long_wq = alloc_workqueue("events_long", 0, 0);
system_nrt_wq = alloc_workqueue("events_nrt", WQ_NON_REENTRANT, 0);
system_unbound_wq = alloc_workqueue("events_unbound", WQ_UNBOUND,
WQ_UNBOUND_MAX_ACTIVE);
system_freezable_wq = alloc_workqueue("events_freezable",
WQ_FREEZABLE, 0);
BUG_ON(!system_wq || !system_long_wq || !system_nrt_wq ||
!system_unbound_wq || !system_freezable_wq);
return 0;
}
early_initcall(init_workqueues);
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