lkml.org 
[lkml]   [2007]   [Jan]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH, RFC] reimplement flush_workqueue()
    On Thu, 4 Jan 2007 17:29:36 +0300
    Oleg Nesterov <oleg@tv-sign.ru> wrote:

    > > In brief:
    > >
    > > keventd thread hotplug thread
    > > -------------- --------------
    > >
    > > run_workqueue()
    > > |
    > > work_fn()
    > > |
    > > flush_workqueue()
    > > |
    > > flush_cpu_workqueue
    > > | cpu_down()
    > > mutex_unlock(wq_mutex); |
    > > (above opens window for hotplug) mutex_lock(wq_mutex);
    > > | /* bring down cpu */
    > > wait_for_completition(); notifier(CPU_DEAD, ..)
    > > | workqueue_cpu_callback
    > > | cleanup_workqueue_thread
    > > | kthread_stop()
    > > |
    > > |
    > > mutex_lock(wq_mutex); <- Can deadlock
    > >
    > >
    > > The kthread_stop() will wait for keventd() thread to exit, but keventd()
    > > is blocked on mutex_lock(wq_mutex) leading to a deadlock.

    This?


    --- a/kernel/workqueue.c~flush_workqueue-use-preempt_disable-to-hold-off-cpu-hotplug
    +++ a/kernel/workqueue.c
    @@ -419,18 +419,22 @@ static void flush_cpu_workqueue(struct c
    * Probably keventd trying to flush its own queue. So simply run
    * it by hand rather than deadlocking.
    */
    - mutex_unlock(&workqueue_mutex);
    + preempt_enable();
    + /*
    + * We can still touch *cwq here because we are keventd, and
    + * hot-unplug will be waiting us to exit.
    + */
    run_workqueue(cwq);
    - mutex_lock(&workqueue_mutex);
    + preempt_disable();
    } else {
    struct wq_barrier barr;

    init_wq_barrier(&barr);
    __queue_work(cwq, &barr.work);

    - mutex_unlock(&workqueue_mutex);
    + preempt_enable(); /* Can no longer touch *cwq */
    wait_for_completion(&barr.done);
    - mutex_lock(&workqueue_mutex);
    + preempt_disable();
    }
    }

    @@ -449,7 +453,7 @@ static void flush_cpu_workqueue(struct c
    */
    void fastcall flush_workqueue(struct workqueue_struct *wq)
    {
    - mutex_lock(&workqueue_mutex);
    + preempt_disable(); /* CPU hotplug */
    if (is_single_threaded(wq)) {
    /* Always use first cpu's area. */
    flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu));
    @@ -459,7 +463,7 @@ void fastcall flush_workqueue(struct wor
    for_each_online_cpu(cpu)
    flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
    }
    - mutex_unlock(&workqueue_mutex);
    + preempt_enable();
    }
    EXPORT_SYMBOL_GPL(flush_workqueue);

    _
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-01-04 18:23    [W:0.026 / U:0.108 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site