Mark it so by renaming __mutex_lock_check_stamp().
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420573509-24774-2-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The original purpose of rq::skip_clock_update was to avoid 'costly' clock
updates for back to back wakeup-preempt pairs. The big problem with it
has always been that the rq variable is unaware of the context and
causes indiscrimiate clock skips.
Rework the entire thing and create a sense of context by only allowing
schedule() to skip clock updates. (XXX can we measure the cost of the
added store?)
By ensuring only schedule can ever skip an update, we guarantee we're
never more than 1 tick behind on the update.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: umgwanakikbuti@gmail.com
Link: http://lkml.kernel.org/r/20150105103554.432381549@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
rq->clock{,_task} are serialized by rq->lock, verify this.
One immediate fail is the usage in scale_rt_capability, so 'annotate'
that for now, there's more 'funny' there. Maybe change rq->lock into a
raw_seqlock_t?
(Only 32-bit is affected)
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150105103554.361872747@infradead.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: umgwanakikbuti@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Search all usage of p->sched_class in sched/core.c, no one check it
before use, so it seems that every task must belong to one sched_class.
Signed-off-by: Yao Dongdong <yaodongdong@huawei.com>
[ Moved the early class assignment to make it boot. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1419835303-28958-1-git-send-email-yaodongdong@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Child has the same decay_count as parent. If it's not zero,
we add it to parent's cfs_rq->removed_load:
wake_up_new_task()->set_task_cpu()->migrate_task_rq_fair().
Child's load is a just garbade after copying of parent,
it hasn't been on cfs_rq yet, and it must not be added to
cfs_rq::removed_load in migrate_task_rq_fair().
The patch moves sched_entity::avg::decay_count intialization
in sched_fork(). So, migrate_task_rq_fair() does not change
removed_load.
Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418644618.6074.13.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
"struct task_struct"->state is "volatile long" and __ffs() warns that
"Undefined if no bit exists, so code should check against 0 first."
Therefore, at expression
state = p->state ? __ffs(p->state) + 1 : 0;
in sched_show_task(), CPU might see "p->state" before "?" as "non-zero"
but "p->state" after "?" as "zero", which could result in
"state >= sizeof(stat_nam)" being true and bogus '?' is printed.
This patch changes "state" from "unsigned int" to "unsigned long" and
save "p->state" before calling __ffs(), in order to avoid potential call
to __ffs(0).
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/201412052131.GCE35924.FVHFOtLOJOMQFS@I-love.SAKURA.ne.jp
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Sometimes a "BUG: sleeping function called from invalid context"
message is not indicative of locking problems, but is the result
of a stack overflow corrupting the thread info.
Witness http://oss.sgi.com/archives/xfs/2014-02/msg00325.html
for example, which took a few go-rounds to sort out.
If we're printing the warning, things are wonky already, and
it'd be informative to check for the stack end corruption at this
point, too.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/5490B158.4060005@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In __synchronize_entity_decay(), if "decays" happens to be zero,
se->avg.decay_count will not be zeroed, holding the positive value
assigned when dequeued last time.
This is problematic in the following case:
If this runnable task is CFS-balanced to other CPUs soon afterwards,
migrate_task_rq_fair() will treat it as a blocked task due to its
non-zero decay_count, thereby adding its load to cfs_rq->removed_load
wrongly.
Thus, we must zero se->avg.decay_count in this case as well.
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418745509-2609-1-git-send-email-pang.xunlei@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull scheduler fixes from Ingo Molnar:
"Misc fixes: group scheduling corner case fix, two deadline scheduler
fixes, effective_load() overflow fix, nested sleep fix, 6144 CPUs
system fix"
* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/fair: Fix RCU stall upon -ENOMEM in sched_create_group()
sched/deadline: Avoid double-accounting in case of missed deadlines
sched/deadline: Fix migration of SCHED_DEADLINE tasks
sched: Fix odd values in effective_load() calculations
sched, fanotify: Deal with nested sleeps
sched: Fix KMALLOC_MAX_SIZE overflow during cpumask allocation
Pull perf fixes from Ingo Molnar:
"Mostly tooling fixes, but also some kernel side fixes: uncore PMU
driver fix, user regs sampling fix and an instruction decoder fix that
unbreaks PEBS precise sampling"
* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf/x86/uncore/hsw-ep: Handle systems with only two SBOXes
perf/x86_64: Improve user regs sampling
perf: Move task_pt_regs sampling into arch code
x86: Fix off-by-one in instruction decoder
perf hists browser: Fix segfault when showing callchain
perf callchain: Free callchains when hist entries are deleted
perf hists: Fix children sort key behavior
perf diff: Fix to sort by baseline field by default
perf list: Fix --raw-dump option
perf probe: Fix crash in dwarf_getcfi_elf
perf probe: Fix to fall back to find probe point in symbols
perf callchain: Append callchains only when requested
perf ui/tui: Print backtrace symbols when segfault occurs
perf report: Show progress bar for output resorting
Pull locking fixes from Ingo Molnar:
"A liblockdep fix and a mutex_unlock() mutex-debugging fix"
* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
mutex: Always clear owner field upon mutex_unlock()
tools/liblockdep: Fix debug_check thinko in mutex destroy
Currently, rcutorture's Reader Batch checks measure from the end of
the previous grace period to the end of the current one. This commit
tightens up these checks by measuring from the start and end of the same
grace period. This involves adding rcu_batches_started() and friends
corresponding to the existing rcu_batches_completed() and friends.
We leave SRCU alone for the moment, as it does not yet have a way of
tracking both ends of its grace periods.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that the return type of rcu_batches_completed() and friends matches
that of the rcu_torture_ops structure's ->completed field, the wrapper
functions can be deleted. This commit carries out that deletion, while
also wiring "sched"'s ->completed field to rcu_batches_completed_sched().
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The counter returned by the various ->completed functions is subject to
overflow, which means that subtracting two such counters might result
in overflow, which invokes undefined behavior in the C standard. This
commit therefore changes these functions and variables to unsigned to
avoid this undefined behavior.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Long ago, the various ->completed fields were of type long, but now are
unsigned long due to signed-integer-overflow concerns. However, the
various _batches_completed() functions remained of type long, even though
their only purpose in life is to return the corresponding ->completed
field. This patch cleans this up by changing these functions' return
types to unsigned long.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cleanups
kdb: Remove unused command flags, repeat flags and KDB_REPEAT_NONE
Fixes
kgdb/kdb: Allow access on a single core, if a CPU round up is deemed
impossible, which will allow inspection of the now "trashed" kernel
kdb: Add enable mask for the command groups
kdb: access controls to restrict sensitive commands
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Merge tag 'for_linus-3.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb
Pull kgdb/kdb fixes from Jason Wessel:
"These have been around since 3.17 and in kgdb-next for the last 9
weeks and some will go back to -stable.
Summary of changes:
Cleanups
- kdb: Remove unused command flags, repeat flags and KDB_REPEAT_NONE
Fixes
- kgdb/kdb: Allow access on a single core, if a CPU round up is
deemed impossible, which will allow inspection of the now "trashed"
kernel
- kdb: Add enable mask for the command groups
- kdb: access controls to restrict sensitive commands"
* tag 'for_linus-3.19-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/jwessel/kgdb:
kernel/debug/debug_core.c: Logging clean-up
kgdb: timeout if secondary CPUs ignore the roundup
kdb: Allow access to sensitive commands to be restricted by default
kdb: Add enable mask for groups of commands
kdb: Categorize kdb commands (similar to SysRq categorization)
kdb: Remove KDB_REPEAT_NONE flag
kdb: Use KDB_REPEAT_* values as flags
kdb: Rename kdb_register_repeat() to kdb_register_flags()
kdb: Rename kdb_repeat_t to kdb_cmdflags_t, cmd_repeat to cmd_flags
kdb: Remove currently unused kdbtab_t->cmd_flags
Currently if DEBUG_MUTEXES is enabled, the mutex->owner field is only
cleared iff debug_locks is active. This exposes a race to other users of
the field where the mutex->owner may be still set to a stale value,
potentially upsetting mutex_spin_on_owner() among others.
References: https://bugs.freedesktop.org/show_bug.cgi?id=87955
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1420540175-30204-1-git-send-email-chris@chris-wilson.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The dl_runtime_exceeded() function is supposed to ckeck if
a SCHED_DEADLINE task must be throttled, by checking if its
current runtime is <= 0. However, it also checks if the
scheduling deadline has been missed (the current time is
larger than the current scheduling deadline), further
decreasing the runtime if this happens.
This "double accounting" is wrong:
- In case of partitioned scheduling (or single CPU), this
happens if task_tick_dl() has been called later than expected
(due to small HZ values). In this case, the current runtime is
also negative, and replenish_dl_entity() can take care of the
deadline miss by recharging the current runtime to a value smaller
than dl_runtime
- In case of global scheduling on multiple CPUs, scheduling
deadlines can be missed even if the task did not consume more
runtime than expected, hence penalizing the task is wrong
This patch fix this problem by throttling a SCHED_DEADLINE task
only when its runtime becomes negative, and not modifying the runtime
Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@gmail.com>
Cc: <stable@vger.kernel.org>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418813432-20797-3-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar <mingo@kernel.org>
According to global EDF, tasks should be migrated between runqueues
without checking if their scheduling deadlines and runtimes are valid.
However, SCHED_DEADLINE currently performs such a check:
a migration happens doing:
deactivate_task(rq, next_task, 0);
set_task_cpu(next_task, later_rq->cpu);
activate_task(later_rq, next_task, 0);
which ends up calling dequeue_task_dl(), setting the new CPU, and then
calling enqueue_task_dl().
enqueue_task_dl() then calls enqueue_dl_entity(), which calls
update_dl_entity(), which can modify scheduling deadline and runtime,
breaking global EDF scheduling.
As a result, some of the properties of global EDF are not respected:
for example, a taskset {(30, 80), (40, 80), (120, 170)} scheduled on
two cores can have unbounded response times for the third task even
if 30/80+40/80+120/170 = 1.5809 < 2
This can be fixed by invoking update_dl_entity() only in case of
wakeup, or if this is a new SCHED_DEADLINE task.
Signed-off-by: Luca Abeni <luca.abeni@unitn.it>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@gmail.com>
Cc: <stable@vger.kernel.org>
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1418813432-20797-2-git-send-email-luca.abeni@unitn.it
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In effective_load, we have (long w * unsigned long tg->shares) / long W,
when w is negative, it is cast to unsigned long and hence the product is
insanely large. Fix this by casting tg->shares to long.
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141219002956.GA25405@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
On x86_64, at least, task_pt_regs may be only partially initialized
in many contexts, so x86_64 should not use it without extra care
from interrupt context, let alone NMI context.
This will allow x86_64 to override the logic and will supply some
scratch space to use to make a cleaner copy of user regs.
Tested-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: chenggang.qcg@taobao.com
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mark Salter <msalter@redhat.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Will Deacon <will.deacon@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/e431cd4c18c2e1c44c774f10758527fb2d1025c4.1420396372.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
wait_consider_task() checks EXIT_ZOMBIE after EXIT_DEAD/EXIT_TRACE and
both checks can fail if we race with EXIT_ZOMBIE -> EXIT_DEAD/EXIT_TRACE
change in between, gcc needs to reload p->exit_state after
security_task_wait(). In this case ->notask_error will be wrongly
cleared and do_wait() can hang forever if it was the last eligible
child.
Many thanks to Arne who carefully investigated the problem.
Note: this bug is very old but it was pure theoretical until commit
b3ab03160dfa ("wait: completely ignore the EXIT_DEAD tasks"). Before
this commit "-O2" was probably enough to guarantee that compiler won't
read ->exit_state twice.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Arne Goedeke <el@laramies.com>
Tested-by: Arne Goedeke <el@laramies.com>
Cc: <stable@vger.kernel.org> [3.15+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Verify that the frequency value from userspace is valid and makes sense.
Unverified values can cause overflows later on.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
[jstultz: Fix up bug for negative values and drop redunent cap check]
Signed-off-by: John Stultz <john.stultz@linaro.org>
An unvalidated user input is multiplied by a constant, which can result in
an undefined behaviour for large values. While this is validated later,
we should avoid triggering undefined behaviour.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
[jstultz: include trivial milisecond->microsecond correction noticed
by Andy]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Subtle race conditions can result if a CPU stays in dyntick-idle mode
long enough for the ->gpnum and ->completed fields to wrap. For
example, consider the following sequence of events:
o CPU 1 encounters a quiescent state while waiting for grace period
5 to complete, but then enters dyntick-idle mode.
o While CPU 1 is in dyntick-idle mode, the grace-period counters
wrap around so that the grace period number is now 4.
o Just as CPU 1 exits dyntick-idle mode, grace period 4 completes
and grace period 5 begins.
o The quiescent state that CPU 1 passed through during the old
grace period 5 looks like it applies to the new grace period
5. Therefore, the new grace period 5 completes without CPU 1
having passed through a quiescent state.
This could clearly be a fatal surprise to any long-running RCU read-side
critical section that happened to be running on CPU 1 at the time. At one
time, this was not a problem, given that it takes significant time for
the grace-period counters to overflow even on 32-bit systems. However,
with the advent of NO_HZ_FULL and SMP embedded systems, arbitrarily long
idle periods are now becoming quite feasible. It is therefore time to
close this race.
This commit therefore avoids this race condition by having the
quiescent-state forcing code detect when a CPU is falling too far
behind, and setting a new rcu_data field ->gpwrap when this happens.
Whenever this new ->gpwrap field is set, the CPU's ->gpnum and ->completed
fields are known to be untrustworthy, and can be ignored, along with
any associated quiescent states.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The current RCU CPU stall warning code will print "Stall ended before
state dump start" any time that the stall-warning code is triggered on
a CPU that has already reported a quiescent state for the current grace
period and if all quiescent states have been reported for the current
grace period. However, a true stall can result in these symptoms, for
example, by preventing RCU's grace-period kthreads from ever running
This commit therefore checks for this condition, reporting the end of
the stall only if one of the grace-period counters has actually advanced.
Otherwise, it reports the last time that the grace-period kthread made
meaningful progress. (In normal situations, the grace-period kthread
should make meaningful progress at least every jiffies_till_next_fqs
jiffies.)
Reported-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Miroslav Benes <mbenes@suse.cz>
One way that an RCU CPU stall warning can happen is if the grace-period
kthread is not allowed to execute. One proxy for this kthread's
forward progress is the number of force-quiescent-state (fqs) scans.
This commit therefore adds the number of fqs scans to the RCU CPU stall
warning printouts when CONFIG_RCU_CPU_STALL_INFO=y.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
SRCU is not necessary to be compiled by default in all cases. For tinification
efforts not compiling SRCU unless necessary is desirable.
The current patch tries to make compiling SRCU optional by introducing a new
Kconfig option CONFIG_SRCU which is selected when any of the components making
use of SRCU are selected.
If we do not select CONFIG_SRCU, srcu.o will not be compiled at all.
text data bss dec hex filename
2007 0 0 2007 7d7 kernel/rcu/srcu.o
Size of arch/powerpc/boot/zImage changes from
text data bss dec hex filename
831552 64180 23944 919676 e087c arch/powerpc/boot/zImage : before
829504 64180 23952 917636 e0084 arch/powerpc/boot/zImage : after
so the savings are about ~2000 bytes.
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
CC: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: resolve conflict due to removal of arch/ia64/kvm/Kconfig. ]
When rcutorture used only the low-order 32 bits of the grace-period
number, it was not a problem for SRCU to use a 32-bit completed field.
However, rcutorture now uses the full 64 bits on 64-bit systems, so
this commit converts SRCU's ->completed field to unsigned long so as to
provide 64 bits on 64-bit systems.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The RCU callback lists are initialized in both rcu_boot_init_percpu_data()
and rcu_init_percpu_data(). The former is intended for initializing
immutable data, so this commit removes the initialization from
rcu_boot_init_percpu_data() and leaves it in rcu_init_percpu_data().
This change prepares for permitting callbacks to be queued very early
in boot.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that blocked tasks are no longer migrated to the root rcu_node
structure, there is no need to scan the root rcu_node structure for
blocked tasks stalling the current grace period. This commit therefore
removes this scan.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The patch dfeb9765ce3c ("Allow post-unlock reference for rt_mutex")
ensured rcu-boost safe even the rt_mutex has post-unlock reference.
But rt_mutex allowing post-unlock reference is definitely a bug and it was
fixed by the commit 27e35715df54 ("rtmutex: Plug slow unlock race").
This fix made the previous patch (dfeb9765ce3c) useless.
And even worse, the priority-inversion introduced by the the previous
patch still exists.
rcu_read_unlock_special() {
rt_mutex_unlock(&rnp->boost_mtx);
/* Priority-Inversion:
* the current task had been deboosted and preempted as a low
* priority task immediately, it could wait long before reschedule in,
* and the rcu-booster also waits on this low priority task and sleeps.
* This priority-inversion makes rcu-booster can't work
* as expected.
*/
complete(&rnp->boost_completion);
}
Just revert the patch to avoid it.
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_cleanup_dead_cpu() function (called after a CPU has gone
completely offline) has not reported a quiescent state because there
was probably at least one synchronize_rcu() between the time the CPU
went offline and the CPU_DEAD notifier, and this would have detected
the CPU's offline state via quiescent-state forcing. However, the plan
is for CPUs to take themselves offline, at which point it makes sense
for them to report their own quiescent state. This commit makes this
change in preparation for the new CPU-hotplug setup.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
When rcu_boost_kthread_setaffinity() sees that all CPUs for a given
rcu_node structure are now offline, it affinities the corresponding
RCU-boost ("rcub") kthread away from those CPUs. This is pointless
because the kthread cannot run on those offline CPUs in any case.
This commit therefore removes this unneeded code.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Because there is no longer any preempted tasks on the root rcu_node, and
because there is no longer ever an rcub kthread for the root rcu_node,
this commit drops the code in force_qs_rnp() that attempts to awaken
the non-existent root rcub kthread. This is strictly a performance
enhancement, removing a root rcu_node ->lock acquisition and release
along with some tests in rcu_initiate_boost(), ending with the test that
notes that there is no rcub kthread.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that offlining CPUs no longer moves leaf rcu_node structures'
->blkd_tasks lists to the root, there is no way for the root rcu_node
structure's ->blkd_task list to be nonempty, unless the root node is also
the sole leaf node. This commit therefore refrains from creating an rcub
kthread for the root rcu_node structure unless it is also the sole leaf.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Given that there is now arcu_preempt_has_tasks() function that checks
to see if the ->blkd_tasks list is non-empty, this commit makes use of it.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Now that we are not migrating callbacks, there is no need to hold the
->orphan_lock across the the ->qsmaskinit bit-clearing process.
This commit therefore releases ->orphan_lock immediately after adopting
the orphaned RCU callbacks.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
When the last CPU associated with a given leaf rcu_node structure
goes offline, something must be done about the tasks queued on that
rcu_node structure. Each of these tasks has been preempted on one of
the leaf rcu_node structure's CPUs while in an RCU read-side critical
section that it have not yet exited. Handling these tasks is the job of
rcu_preempt_offline_tasks(), which migrates them from the leaf rcu_node
structure to the root rcu_node structure.
Unfortunately, this migration has to be done one task at a time because
each tasks allegiance must be shifted from the original leaf rcu_node to
the root, so that future attempts to deal with these tasks will acquire
the root rcu_node structure's ->lock rather than that of the leaf.
Worse yet, this migration must be done with interrupts disabled, which
is not so good for realtime response, especially given that there is
no bound on the number of tasks on a given rcu_node structure's list.
(OK, OK, there is a bound, it is just that it is unreasonably large,
especially on 64-bit systems.) This was not considered a problem back
when rcu_preempt_offline_tasks() was first written because realtime
systems were assumed not to do CPU-hotplug operations while real-time
applications were running. This assumption has proved of dubious validity
given that people are starting to run multiple realtime applications
on a single SMP system and that it is common practice to offline then
online a CPU before starting its real-time application in order to clear
extraneous processing off of that CPU. So we now need CPU hotplug
operations to avoid undue latencies.
This commit therefore avoids migrating these tasks, instead letting
them be dequeued one by one from the original leaf rcu_node structure
by rcu_read_unlock_special(). This means that the clearing of bits
from the upper-level rcu_node structures must be deferred until the
last such task has been dequeued, because otherwise subsequent grace
periods won't wait on them. This commit has the beneficial side effect
of simplifying the CPU-hotplug code for TREE_PREEMPT_RCU, especially in
CONFIG_RCU_BOOST builds.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit causes rcu_read_unlock_special() to propagate ->qsmaskinit
bit clearing up the rcu_node tree once a given rcu_node structure's
blkd_tasks list becomes empty. This is the final commit in preparation
for the rework of RCU priority boosting: It enables preempted tasks to
remain queued on their rcu_node structure even after all of that rcu_node
structure's CPUs have gone offline.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit abstracts rcu_cleanup_dead_rnp() from rcu_cleanup_dead_cpu()
in preparation for the rework of RCU priority boosting. This new function
will be invoked from rcu_read_unlock_special() in the reworked scheme,
which is why rcu_cleanup_dead_rnp() assumes that the leaf rcu_node
structure's ->qsmaskinit field has already been updated.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit undertakes a simple variable renaming to make way for
some rework of RCU priority boosting.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit prevents random compiler optimizations by applying
ACCESS_ONCE() to lockless accesses.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The 48a7639ce80c ("rcu: Make callers awaken grace-period kthread")
removed the irq_work_queue(), so the TREE_RCU doesn't need
irq work any more. This commit therefore updates RCU's Kconfig and
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
The rcu_barrier() no-callbacks check for no-CBs CPUs has race conditions.
It checks a given CPU's lists of callbacks, and if all three no-CBs lists
are empty, ignores that CPU. However, these three lists could potentially
be empty even when callbacks are present if the check executed just as
the callbacks were being moved from one list to another. It turns out
that recent versions of rcutorture can spot this race.
This commit plugs this hole by consolidating the per-list counts of
no-CBs callbacks into a single count, which is incremented before
the corresponding callback is posted and after it is invoked. Then
rcu_barrier() checks this single count to reliably determine whether
the corresponding CPU has no-CBs callbacks.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and expedited
grace periods") introduced another problem that can easily be reproduced by
starting/stopping cpus in a loop.
E.g.:
for i in `seq 5000`; do
echo 1 > /sys/devices/system/cpu/cpu1/online
echo 0 > /sys/devices/system/cpu/cpu1/online
done
Will result in:
INFO: task /cpu_start_stop:1 blocked for more than 120 seconds.
Call Trace:
([<00000000006a028e>] __schedule+0x406/0x91c)
[<0000000000130f60>] cpu_hotplug_begin+0xd0/0xd4
[<0000000000130ff6>] _cpu_up+0x3e/0x1c4
[<0000000000131232>] cpu_up+0xb6/0xd4
[<00000000004a5720>] device_online+0x80/0xc0
[<00000000004a57f0>] online_store+0x90/0xb0
...
And a deadlock.
Problem is that if the last ref in put_online_cpus() can't get the
cpu_hotplug.lock the puts_pending count is incremented, but a sleeping
active_writer might never be woken up, therefore never exiting the loop in
cpu_hotplug_begin().
This fix removes puts_pending and turns refcount into an atomic variable. We
also introduce a wait queue for the active_writer, to avoid possible races and
use-after-free. There is no need to take the lock in put_online_cpus() anymore.
Can't reproduce it with this fix.
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
