Commit b3104104 authored Feb 19, 2013 by Lai Jiangshan Committed by Tejun Heo Mar 04, 2013

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>

parent f36dc67b

kernel/workqueue.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2357,8 +2357,8 @@ repeat:
		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 @@ repeat:
		if (keep_working(pool))
		wake_up_worker(pool);

		rescuer->pool = NULL;
		spin_unlock_irq(&pool->lock);
		}

kernel/workqueue_internal.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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 */