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workqueues: shrink cpu_populated_map when CPU dies

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When cpu_populated_map was introduced, it was supposed that cwq->thread can
survive after CPU_DEAD, that is why we never shrink cpu_populated_map.

This is not very nice, we can safely remove the already dead CPU from the map.
 The only required change is that destroy_workqueue() must hold the hotplug
lock until it destroys all cwq->thread's, to protect the cpu_populated_map.
We could make the local copy of cpu mask and drop the lock, but
sizeof(cpumask_t) may be very large.

Also, fix the comment near queue_work().  Unless _cpu_down() happens we do
guarantee the cpu-affinity of the work_struct, and we have users which rely on
this.

[akpm@linux-foundation.org: repair comment]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2008-04-29 01:00:27 -07:00 committed by Linus Torvalds
parent 786083667e
commit 00dfcaf748
1 changed files with 9 additions and 4 deletions
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13
kernel/workqueue.c
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@ -158,8 +158,8 @@ static void __queue_work(struct cpu_workqueue_struct *cwq,
*
* Returns 0 if @work was already on a queue, non-zero otherwise.
*
* We queue the work to the CPU it was submitted, but there is no
* guarantee that it will be processed by that CPU.
* We queue the work to the CPU on which it was submitted, but if the CPU dies
* it can be processed by another CPU.
*/
int queue_work(struct workqueue_struct *wq, struct work_struct *work)
{
@ -815,12 +815,12 @@ void destroy_workqueue(struct workqueue_struct *wq)
spin_lock(&workqueue_lock);
list_del(&wq->list);
spin_unlock(&workqueue_lock);
put_online_cpus();
for_each_cpu_mask(cpu, *cpu_map) {
cwq = per_cpu_ptr(wq->cpu_wq, cpu);
cleanup_workqueue_thread(cwq, cpu);
}
put_online_cpus();
free_percpu(wq->cpu_wq);
kfree(wq);
@ -838,7 +838,6 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
action &= ~CPU_TASKS_FROZEN;
switch (action) {
case CPU_UP_PREPARE:
cpu_set(cpu, cpu_populated_map);
}
@ -866,6 +865,12 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
}
}
switch (action) {
case CPU_UP_CANCELED:
case CPU_DEAD:
cpu_clear(cpu, cpu_populated_map);
}
return NOTIFY_OK;
}