workqueues: shrink cpu_populated_map when CPU dies (00dfcaf7) · Commits · 戴 / test

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>

kernel/workqueue.c

+9 −4

Original line number	Diff line number	Diff line
		@@ -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;
		}

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