Commit c9178087 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: perform non-reentrancy test when queueing to unbound workqueues too 



Because per-cpu workqueues have multiple pwqs (pool_workqueues) to
serve the CPUs, to guarantee that a single work item isn't queued on
one pwq while still executing another, __queue_work() takes a look at
the previous pool the target work item was on and if it's still
executing there, queue the work item on that pool.

To support changing workqueue_attrs on the fly, unbound workqueues too
will have multiple pwqs and thus need non-reentrancy test when
queueing.  This patch modifies __queue_work() such that the reentrancy
test is performed regardless of the workqueue type.

per_cpu_ptr(wq->cpu_pwqs, cpu) used to be used to determine the
matching pwq for the last pool.  This can't be used for unbound
workqueues and is replaced with worker->current_pwq which also happens
to be simpler.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reviewed-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
parent 75ccf595

kernel/workqueue.c

+19 −23
Original line number Diff line number Diff line
@@ -1209,6 +1209,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
			 struct work_struct *work)

{

	struct pool_workqueue *pwq;

	struct worker_pool *last_pool;

	struct list_head *worklist;

	unsigned int work_flags;

	unsigned int req_cpu = cpu;
@@ -1228,22 +1229,21 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
	    WARN_ON_ONCE(!is_chained_work(wq)))

		return;



	/* determine the pwq to use */

	/* pwq which will be used unless @work is executing elsewhere */

	if (!(wq->flags & WQ_UNBOUND)) {

		struct worker_pool *last_pool;



		if (cpu == WORK_CPU_UNBOUND)

			cpu = raw_smp_processor_id();

		pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);

	} else {

		pwq = first_pwq(wq);

	}



	/*

		 * It's multi cpu.  If @work was previously on a different

		 * cpu, it might still be running there, in which case the

		 * work needs to be queued on that cpu to guarantee

		 * non-reentrancy.

	 * If @work was previously on a different pool, it might still be

	 * running there, in which case the work needs to be queued on that

	 * pool to guarantee non-reentrancy.

	 */

		pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);

	last_pool = get_work_pool(work);



	if (last_pool && last_pool != pwq->pool) {

		struct worker *worker;
@@ -1252,7 +1252,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
		worker = find_worker_executing_work(last_pool, work);



		if (worker && worker->current_pwq->wq == wq) {

				pwq = per_cpu_ptr(wq->cpu_pwqs, last_pool->cpu);

			pwq = worker->current_pwq;

		} else {

			/* meh... not running there, queue here */

			spin_unlock(&last_pool->lock);
@@ -1261,10 +1261,6 @@ static void __queue_work(int cpu, struct workqueue_struct *wq, 
	} else {

		spin_lock(&pwq->pool->lock);

	}

	} else {

		pwq = first_pwq(wq);

		spin_lock(&pwq->pool->lock);

	}



	/* pwq determined, queue */

	trace_workqueue_queue_work(req_cpu, pwq, work);

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