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workqueue: better define synchronization rule around rescuer->pool updates
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>
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@ -2357,8 +2357,8 @@ static int rescuer_thread(void *__rescuer)
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mayday_clear_cpu(cpu, wq->mayday_mask);
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/* migrate to the target cpu if possible */
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rescuer->pool = pool;
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worker_maybe_bind_and_lock(pool);
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rescuer->pool = pool;
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/*
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* Slurp in all works issued via this workqueue and
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@ -2379,6 +2379,7 @@ static int rescuer_thread(void *__rescuer)
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if (keep_working(pool))
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wake_up_worker(pool);
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rescuer->pool = NULL;
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spin_unlock_irq(&pool->lock);
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}
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@ -32,6 +32,7 @@ struct worker {
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struct list_head scheduled; /* L: scheduled works */
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struct task_struct *task; /* I: worker task */
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struct worker_pool *pool; /* I: the associated pool */
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/* L: for rescuers */
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/* 64 bytes boundary on 64bit, 32 on 32bit */
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unsigned long last_active; /* L: last active timestamp */
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unsigned int flags; /* X: flags */
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