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workqueue: better define synchronization rule around rescuer->pool updates

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Rescuers visit different worker_pools to process work items from pools
under pressure.  Currently, rescuer->pool is updated outside any
locking and when an outsider looks at a rescuer, there's no way to
tell when and whether rescuer->pool is gonna change.  While this
doesn't currently cause any problem, it is nasty.

With recent worker_maybe_bind_and_lock() changes, we can move
rescuer->pool updates inside pool locks such that if rescuer->pool
equals a locked pool, it's guaranteed to stay that way until the pool
is unlocked.

Move rescuer->pool inside pool->lock.

This patch doesn't introduce any visible behavior difference.

tj: Updated the description.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Lai Jiangshan 2013-02-19 12:17:02 -08:00 committed by Tejun Heo
parent f36dc67b27
commit b31041042a
2 changed files with 3 additions and 1 deletions
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3
kernel/workqueue.c
View file

@ -2357,8 +2357,8 @@ static int rescuer_thread(void *__rescuer)
mayday_clear_cpu(cpu, wq->mayday_mask);
/* migrate to the target cpu if possible */
rescuer->pool = pool;
worker_maybe_bind_and_lock(pool);
rescuer->pool = pool;
/*
* Slurp in all works issued via this workqueue and
@ -2379,6 +2379,7 @@ static int rescuer_thread(void *__rescuer)
if (keep_working(pool))
wake_up_worker(pool);
rescuer->pool = NULL;
spin_unlock_irq(&pool->lock);
}

1
kernel/workqueue_internal.h
View file

@ -32,6 +32,7 @@ struct worker {
struct list_head scheduled; /* L: scheduled works */
struct task_struct *task; /* I: worker task */
struct worker_pool *pool; /* I: the associated pool */
/* L: for rescuers */
/* 64 bytes boundary on 64bit, 32 on 32bit */
unsigned long last_active; /* L: last active timestamp */
unsigned int flags; /* X: flags */