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connector/cn_proc: Protect send_msg() with a local lock

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send_msg() disables preemption to avoid out-of-order messages. As the
code inside the preempt disabled section acquires regular spinlocks,
which are converted to 'sleeping' spinlocks on a PREEMPT_RT kernel and
eventually calls into a memory allocator, this conflicts with the RT
semantics.

Convert it to a local_lock which allows RT kernels to substitute them with
a real per CPU lock. On non RT kernels this maps to preempt_disable() as
before. No functional change.

[bigeasy: Patch description]

Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20200527201119.1692513-6-bigeasy@linutronix.de
This commit is contained in:
Mike Galbraith 2020-05-27 22:11:17 +02:00 committed by Ingo Molnar
parent fd56200a16
commit 3e92fd7bd2
1 changed files with 14 additions and 7 deletions
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21
drivers/connector/cn_proc.c
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@ -18,6 +18,7 @@
#include <linux/pid_namespace.h> #include <linux/pid_namespace.h>
#include <linux/cn_proc.h> #include <linux/cn_proc.h>
#include <linux/local_lock.h>
/* /*
* Size of a cn_msg followed by a proc_event structure. Since the * Size of a cn_msg followed by a proc_event structure. Since the
@ -38,25 +39,31 @@ static inline struct cn_msg *buffer_to_cn_msg(__u8 *buffer)
static atomic_t proc_event_num_listeners = ATOMIC_INIT(0); static atomic_t proc_event_num_listeners = ATOMIC_INIT(0);
static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC }; static struct cb_id cn_proc_event_id = { CN_IDX_PROC, CN_VAL_PROC };
/* proc_event_counts is used as the sequence number of the netlink message */ /* local_event.count is used as the sequence number of the netlink message */
static DEFINE_PER_CPU(__u32, proc_event_counts) = { 0 }; struct local_event {
local_lock_t lock;
__u32 count;
};
static DEFINE_PER_CPU(struct local_event, local_event) = {
.lock = INIT_LOCAL_LOCK(lock),
};
static inline void send_msg(struct cn_msg *msg) static inline void send_msg(struct cn_msg *msg)
{ {
preempt_disable(); local_lock(&local_event.lock);
msg->seq = __this_cpu_inc_return(proc_event_counts) - 1; msg->seq = __this_cpu_inc_return(local_event.count) - 1;
((struct proc_event *)msg->data)->cpu = smp_processor_id(); ((struct proc_event *)msg->data)->cpu = smp_processor_id();
/* /*
* Preemption remains disabled during send to ensure the messages are * local_lock() disables preemption during send to ensure the messages
* ordered according to their sequence numbers. * are ordered according to their sequence numbers.
* *
* If cn_netlink_send() fails, the data is not sent. * If cn_netlink_send() fails, the data is not sent.
*/ */
cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT); cn_netlink_send(msg, 0, CN_IDX_PROC, GFP_NOWAIT);
preempt_enable(); local_unlock(&local_event.lock);
} }
void proc_fork_connector(struct task_struct *task) void proc_fork_connector(struct task_struct *task)