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Commit e41e704b authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: improve destroy_workqueue() debuggability 



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: default avatarTejun Heo <tj@kernel.org>
parent 972fa1c5

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);



	/*