Re: [PATCH] blk-mq: prevent unmapped hw queue from being scheduled

[Jens Axboe]

On 12/08/2014 05:41 PM, Ming Lei wrote:
> On Wed, Dec 3, 2014 at 7:38 PM, Ming Lei <ming.lei@xxxxxxxxxxxxx> wrote:
> > When one hardware queue has no mapped software queues, it
> > shouldn't have been scheduled. Otherwise WARNING or OOPS
> > can triggered.
> >
> > blk_mq_hw_queue_mapped() helper is introduce for fixing
> > the problem.
> >
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> > ---
> >   block/blk-mq.c |    8 ++++++--
> >   block/blk-mq.h |    5 +++++
> >   2 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index c95abc6..c916ad0 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -599,7 +599,7 @@ static void blk_mq_rq_timer(unsigned long priv)
> >                   * If not software queues are currently mapped to this
> >                   * hardware queue, there's nothing to check
> >                   */
> > -               if (!hctx->nr_ctx || !hctx->tags)
> > +               if (!blk_mq_hw_queue_mapped(hctx))
> >                          continue;
> >
> >                  blk_mq_tag_busy_iter(hctx, blk_mq_check_expired, &data);
> > @@ -819,7 +819,8 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
> >
> >   void blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async)
> >   {
> > -       if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
> > +       if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state) ||
> > +           !blk_mq_hw_queue_mapped(hctx)))
> >                  return;
> >
> >          if (!async) {
> > @@ -926,6 +927,9 @@ static void blk_mq_delay_work_fn(struct work_struct *work)
> >
> >   void blk_mq_delay_queue(struct blk_mq_hw_ctx *hctx, unsigned long msecs)
> >   {
> > +       if (unlikely(!blk_mq_hw_queue_mapped(hctx)))
> > +               return;
> > +
> >          kblockd_schedule_delayed_work_on(blk_mq_hctx_next_cpu(hctx),
> >                          &hctx->delay_work, msecs_to_jiffies(msecs));
> >   }
> > diff --git a/block/blk-mq.h b/block/blk-mq.h
> > index d567d52..206230e 100644
> > --- a/block/blk-mq.h
> > +++ b/block/blk-mq.h
> > @@ -115,4 +115,9 @@ static inline void blk_mq_set_alloc_data(struct blk_mq_alloc_data *data,
> >          data->hctx = hctx;
> >   }
> >
> > +static inline bool blk_mq_hw_queue_mapped(struct blk_mq_hw_ctx *hctx)
> > +{
> > +       return hctx->nr_ctx && hctx->tags;
> > +}
> > +
> >   #endif
>
> Gentle ping...

Picked up for 3.19, sorry for the delay. I'm curious how this queue gets 
scheduled, though. My worry here would be that we are masking a bug that 
should be fixed separately.

--
Jens Axboe

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