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workqueue: drop CPU_DYING notifier operation 

Workqueue used CPU_DYING notification to mark GCWQ_DISASSOCIATED.
This was necessary because workqueue's CPU_DOWN_PREPARE happened
before other DOWN_PREPARE notifiers and workqueue needed to stay
associated across the rest of DOWN_PREPARE.

After the previous patch, workqueue's DOWN_PREPARE happens after
others and can set GCWQ_DISASSOCIATED directly.  Drop CPU_DYING and
let the trustee set GCWQ_DISASSOCIATED after disabling concurrency
management.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
This commit is contained in:
Tejun Heo 2012-07-17 12:39:26 -07:00
parent 6575820221
commit f2d5a0ee06
1 changed files with 13 additions and 16 deletions
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29
kernel/workqueue.c
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@ -1250,11 +1250,11 @@ static void worker_leave_idle(struct worker *worker)
* verbatim as it's best effort and blocking and gcwq may be
* [dis]associated in the meantime.
*
* This function tries set_cpus_allowed() and locks gcwq and verifies
* the binding against GCWQ_DISASSOCIATED which is set during
* CPU_DYING and cleared during CPU_ONLINE, so if the worker enters
* idle state or fetches works without dropping lock, it can guarantee
* the scheduling requirement described in the first paragraph.
* This function tries set_cpus_allowed() and locks gcwq and verifies the
* binding against %GCWQ_DISASSOCIATED which is set during
* %CPU_DOWN_PREPARE and cleared during %CPU_ONLINE, so if the worker
* enters idle state or fetches works without dropping lock, it can
* guarantee the scheduling requirement described in the first paragraph.
*
* CONTEXT:
* Might sleep. Called without any lock but returns with gcwq->lock
@ -3349,6 +3349,12 @@ static int __cpuinit trustee_thread(void *__gcwq)
rc = trustee_wait_event(!gcwq_is_managing_workers(gcwq));
BUG_ON(rc < 0);
/*
* We've claimed all manager positions. Make all workers unbound
* and set DISASSOCIATED. Before this, all workers except for the
* ones which are still executing works from before the last CPU
* down must be on the cpu. After this, they may become diasporas.
*/
for_each_worker_pool(pool, gcwq) {
pool->flags |= POOL_MANAGING_WORKERS;
@ -3359,6 +3365,8 @@ static int __cpuinit trustee_thread(void *__gcwq)
for_each_busy_worker(worker, i, pos, gcwq)
worker->flags |= WORKER_ROGUE;
gcwq->flags |= GCWQ_DISASSOCIATED;
/*
* Call schedule() so that we cross rq->lock and thus can
* guarantee sched callbacks see the rogue flag. This is
@ -3582,16 +3590,6 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
}
break;
case CPU_DYING:
/*
* Before this, the trustee and all workers except for
* the ones which are still executing works from
* before the last CPU down must be on the cpu. After
* this, they'll all be diasporas.
*/
gcwq->flags |= GCWQ_DISASSOCIATED;
break;
case CPU_POST_DEAD:
gcwq->trustee_state = TRUSTEE_BUTCHER;
/* fall through */
@ -3672,7 +3670,6 @@ static int __devinit workqueue_cpu_down_callback(struct notifier_block *nfb,
{
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_DOWN_PREPARE:
case CPU_DYING:
case CPU_POST_DEAD:
return workqueue_cpu_callback(nfb, action, hcpu);
}