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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: Tejun Heo <tj@kernel.org>
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@ -241,6 +241,8 @@ enum {
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WQ_HIGHPRI = 1 << 4, /* high priority */
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WQ_CPU_INTENSIVE = 1 << 5, /* cpu instensive workqueue */
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WQ_DYING = 1 << 6, /* internal: workqueue is dying */
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WQ_MAX_ACTIVE = 512, /* I like 512, better ideas? */
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WQ_MAX_UNBOUND_PER_CPU = 4, /* 4 * #cpus for unbound wq */
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WQ_DFL_ACTIVE = WQ_MAX_ACTIVE / 2,
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@ -87,7 +87,8 @@ enum {
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/*
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* Structure fields follow one of the following exclusion rules.
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*
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* I: Set during initialization and read-only afterwards.
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* I: Modifiable by initialization/destruction paths and read-only for
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* everyone else.
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*
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* P: Preemption protected. Disabling preemption is enough and should
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* only be modified and accessed from the local cpu.
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@ -944,6 +945,9 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
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debug_work_activate(work);
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if (WARN_ON_ONCE(wq->flags & WQ_DYING))
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return;
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/* determine gcwq to use */
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if (!(wq->flags & WQ_UNBOUND)) {
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struct global_cwq *last_gcwq;
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@ -2828,6 +2832,7 @@ void destroy_workqueue(struct workqueue_struct *wq)
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{
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unsigned int cpu;
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wq->flags |= WQ_DYING;
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flush_workqueue(wq);
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/*
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