workqueue: improve destroy_workqueue() debuggability (e41e704b) · Commits · 戴 / test

Now that the worklist is global, having works pending after wq destruction can easily lead to oops and destroy_workqueue() have several BUG_ON()s to catch these cases. Unfortunately, BUG_ON() doesn't tell much about how the work became pending after the final flush_workqueue(). This patch adds WQ_DYING which is set before the final flush begins. If a work is requested to be queued on a dying workqueue, WARN_ON_ONCE() is triggered and the request is ignored. This clearly indicates which caller is trying to queue a work on a dying workqueue and keeps the system working in most cases. Locking rule comment is updated such that the 'I' rule includes modifying the field from destruction path. Signed-off-by:

Tejun Heo <tj@kernel.org>

include/linux/workqueue.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -241,6 +241,8 @@ enum {
		WQ_HIGHPRI = 1 << 4, /* high priority */
		WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */

		WQ_DYING = 1 << 6, /* internal: workqueue is dying */

		WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
		WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
		WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,

kernel/workqueue.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -87,7 +87,8 @@ enum {
		/*
		* Structure fields follow one of the following exclusion rules.
		*
		* I: Set during initialization and read-only afterwards.
		* I: Modifiable by initialization/destruction paths and read-only for
		* everyone else.
		*
		* P: Preemption protected. Disabling preemption is enough and should
		* only be modified and accessed from the local cpu.
		@@ -944,6 +945,9 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,

		debug_work_activate(work);

		if (WARN_ON_ONCE(wq->flags & WQ_DYING))
		return;

		/* determine gcwq to use */
		if (!(wq->flags & WQ_UNBOUND)) {
		struct global_cwq *last_gcwq;
		@@ -2828,6 +2832,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
		{
		unsigned int cpu;

		wq->flags \|= WQ_DYING;
		flush_workqueue(wq);

		/*

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