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Date: Thu, 7 Dec 2006 11:37:00 -0800 From: Andrew Morton <akpm@...l.org> To: Bjorn Helgaas <bjorn.helgaas@...com>, Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Myron Stowe <myron.stowe@...com>, Jens Axboe <axboe@...nel.dk> Subject: Re: workqueue deadlock On Thu, 7 Dec 2006 10:51:48 -0800 Andrew Morton <akpm@...l.org> wrote: > + if (!cpu_online(cpu)) /* oops, CPU got unplugged */ > + goto bail; hm, actually we can pull the same trick with flush_scheduled_work(). Should fix quite a few things... From: Andrew Morton <akpm@...l.org> We have a class of deadlocks where the flush_scheduled_work() caller can get stuck waiting for a work to complete, where that work wants to take workqueue_mutex for some reason. Fix this by not holding workqueue_mutex when waiting for a workqueue to flush. The patch assumes that the per-cpu workqueue won't get freed up while there's a task waiting on cpu_workqueue_struct.work_done. If that can happen, run_workqueue() would crash anyway. Cc: Bjorn Helgaas <bjorn.helgaas@...com> Cc: Ingo Molnar <mingo@...e.hu> Cc: Srivatsa Vaddagiri <vatsa@...ibm.com> Cc: Gautham shenoy <ego@...ibm.com> Signed-off-by: Andrew Morton <akpm@...l.org> --- kernel/workqueue.c | 22 +++++++++++++++++++--- 1 files changed, 19 insertions(+), 3 deletions(-) diff -puN kernel/workqueue.c~workqueue-dont-hold-workqueue_mutex-in-flush_scheduled_work kernel/workqueue.c --- a/kernel/workqueue.c~workqueue-dont-hold-workqueue_mutex-in-flush_scheduled_work +++ a/kernel/workqueue.c @@ -325,14 +325,22 @@ static int worker_thread(void *__cwq) return 0; } -static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) +/* + * If cpu == -1 it's a single-threaded workqueue and the caller does not hold + * workqueue_mutex + */ +static void flush_cpu_workqueue(struct cpu_workqueue_struct *cwq, int cpu) { if (cwq->thread == current) { /* * Probably keventd trying to flush its own queue. So simply run * it by hand rather than deadlocking. */ + if (cpu != -1) + mutex_unlock(&workqueue_mutex); run_workqueue(cwq); + if (cpu != -1) + mutex_lock(&workqueue_mutex); } else { DEFINE_WAIT(wait); long sequence_needed; @@ -344,7 +352,14 @@ static void flush_cpu_workqueue(struct c prepare_to_wait(&cwq->work_done, &wait, TASK_UNINTERRUPTIBLE); spin_unlock_irq(&cwq->lock); + if (cpu != -1) + mutex_unlock(&workqueue_mutex); schedule(); + if (cpu != -1) { + mutex_lock(&workqueue_mutex); + if (!cpu_online(cpu)) + return; /* oops, CPU unplugged */ + } spin_lock_irq(&cwq->lock); } finish_wait(&cwq->work_done, &wait); @@ -373,13 +388,14 @@ void fastcall flush_workqueue(struct wor if (is_single_threaded(wq)) { /* Always use first cpu's area. */ - flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu)); + flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu), + -1); } else { int cpu; mutex_lock(&workqueue_mutex); for_each_online_cpu(cpu) - flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu)); + flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu), cpu); mutex_unlock(&workqueue_mutex); } } _ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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