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    SubjectRe: [PATCH v2] workqueue: lock cwq access in drain_workqueue
    Hello,

    On Fri, Sep 09, 2011 at 07:00:53PM -0400, Thomas Tuttle wrote:
    > Take cwq->gcwq->lock to avoid racing between drain_workqueue checking
    > to make sure the workqueues are empty and cwq_dec_nr_in_flight
    > decrementing and then incrementing nr_active when it activates a
    > delayed work.

    Nice catch. Just few minor nits below.

    > We discovered this when a corner case in one of our drivers resulted in
    > us trying to destroy a workqueue in which the remaining work would
    > always requeue itself again in the same workqueue. We would hit this
    > race condition and trip the BUG_ON on workqueue.c:3080.
    >
    > Signed-off-by: Thomas Tuttle <ttuttle@chromium.org>
    > ---
    > Updated to use bool instead of int (d'oh), and CCed maintainer.
    >
    > kernel/workqueue.c | 8 +++++++-
    > 1 files changed, 7 insertions(+), 1 deletions(-)
    >
    > diff --git a/kernel/workqueue.c b/kernel/workqueue.c
    > index 25fb1b0..0c2e585 100644
    > --- a/kernel/workqueue.c
    > +++ b/kernel/workqueue.c
    > @@ -2412,8 +2412,14 @@ reflush:
    >
    > for_each_cwq_cpu(cpu, wq) {
    > struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
    > + bool cwq_flushed;

    Maybe "drained" would be better?

    > - if (!cwq->nr_active && list_empty(&cwq->delayed_works))
    > + spin_lock_irq(&cwq->gcwq->lock);
    > + cwq_flushed = !cwq->nr_active
    > + && list_empty(&cwq->delayed_works);

    and then this should fit inside 80 column, right?

    Thanks.

    --
    tejun


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