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    SubjectRe: [PATCH] block: In blk_execute_rq_nowait, init rq->end_io before checking for dead queue.
    From
    Tejun, Jens,
    This is a real problem, right? Should we fix it differently?

    Regards,
    Muthu

    On Wed, Jun 6, 2012 at 11:27 PM, Muthu Kumar <muthu.lkml@gmail.com> wrote:
    > On Wed, Jun 6, 2012 at 11:16 PM, Tejun Heo <tj@kernel.org> wrote:
    >> Sorry to be nit-picky but Jens would appreciate proper subject and it
    >> would also be nice to mention the locking change (or even separate
    >> that into a separate patch).
    >
    > No problem. Changed the subject and also added the info about queue
    > lock in the description. Please check.
    >
    > -----------------------
    > blk-exec.c: In blk_execute_rq_nowait(), if the queue is dead, call to
    > done() routine is not made. That will result in blk_execute_rq() stuck
    > in wait_for_completion(). Avoid this by initializing rq->end_io to
    > done() routine before we check for dead queue.
    >
    > Also, in case of dead queue, call the completion routine with queue->lock held.
    >
    >
    > Signed-off-by: Muthukumar Ratty <muthur@gmail.com>
    > CC: Tejun Heo <tj@kernel.org>
    > CC: Jens Axboe <axboe@kernel.dk>
    > CC: James Bottomley <James.Bottomley@hansenpartnership.com>
    >
    > -----------------------
    >
    > diff --git a/block/blk-exec.c b/block/blk-exec.c
    > index fb2cbd5..284bf56 100644
    > --- a/block/blk-exec.c
    > +++ b/block/blk-exec.c
    > @@ -53,16 +53,17 @@ void blk_execute_rq_nowait(struct request_queue
    > *q, struct gendisk *bd_disk,
    >        WARN_ON(irqs_disabled());
    >        spin_lock_irq(q->queue_lock);
    >
    > +       rq->rq_disk = bd_disk;
    > +       rq->end_io = done;
    > +
    >        if (unlikely(blk_queue_dead(q))) {
    > -               spin_unlock_irq(q->queue_lock);
    >                rq->errors = -ENXIO;
    >                if (rq->end_io)
    >                        rq->end_io(rq, rq->errors);
    > +               spin_unlock_irq(q->queue_lock);
    >                return;
    >        }
    >
    > -       rq->rq_disk = bd_disk;
    > -       rq->end_io = done;
    >        __elv_add_request(q, rq, where);
    >        __blk_run_queue(q);
    >        /* the queue is stopped so it won't be run */
    >
    >
    > ------------------------------------
    >
    >
    >
    >
    >
    >
    >
    >>
    >> Thanks.
    >>
    >> --
    >> tejun
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