On Wed, Nov 22, 2017 at 08:04:13AM +0100, Hannes Reinecke wrote:
> On 11/22/2017 06:11 AM, Ming Lei wrote:
> > Now we track legacy requests with .q_usage_counter in commit 055f6e18e08f
> > ("block: Make q_usage_counter also track legacy requests"), but that
> > commit never runs and drains legacy queue before waiting for this counter
> > becoming zero, then IO hang is caused in the test of pulling disk during IO.
> >
> > This patch fixes the issue by draining requests before waiting for
> > q_usage_counter becoming zero.
> >
> > Fixes: 055f6e18e08f("block: Make q_usage_counter also track legacy
> > requests")
> > Cc: Wen Xiong <wenxi...@us.ibm.com>
> > Signed-off-by: Ming Lei <ming....@redhat.com>
> > ---
> > block/blk-core.c | 9 +++++++--
> > block/blk-mq.c | 2 ++
> > block/blk.h | 2 ++
> > 3 files changed, 11 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 1038706edd87..5ae5ea0dca4c 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -562,6 +562,13 @@ static void __blk_drain_queue(struct request_queue *q,
> > bool drain_all)
> > }
> > }
> >
> > +void blk_drain_queue(struct request_queue *q)
> > +{
> > + spin_lock_irq(q->queue_lock);
> > + __blk_drain_queue(q, true);
> > + spin_unlock_irq(q->queue_lock);
> > +}
> > +
> > /**
> > * blk_queue_bypass_start - enter queue bypass mode
> > * @q: queue of interest
> > @@ -689,8 +696,6 @@ void blk_cleanup_queue(struct request_queue *q)
> > */
> > blk_freeze_queue(q);
> > spin_lock_irq(lock);
> > - if (!q->mq_ops)
> > - __blk_drain_queue(q, true);
> > queue_flag_set(QUEUE_FLAG_DEAD, q);
> > spin_unlock_irq(lock);
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index 11097477eeab..3d3797327491 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -161,6 +161,8 @@ void blk_freeze_queue(struct request_queue *q)
> > * exported to drivers as the only user for unfreeze is blk_mq.
> > */
> > blk_freeze_queue_start(q);
> > + if (!q->mq_ops)
> > + blk_drain_queue(q);
> > blk_mq_freeze_queue_wait(q);
> > }
> >
> > diff --git a/block/blk.h b/block/blk.h
> > index 3f1446937aec..442098aa9463 100644
> > --- a/block/blk.h
> > +++ b/block/blk.h
> > @@ -330,4 +330,6 @@ static inline void blk_queue_bounce(struct
> > request_queue *q, struct bio **bio)
> > }
> > #endif /* CONFIG_BOUNCE */
> >
> > +extern void blk_drain_queue(struct request_queue *q);
> > +
> > #endif /* BLK_INTERNAL_H */
> >
> I seem to have missed something.
> Is blk_drain_queue() ever used?
It is always called in blk_cleanup_queue().
Before 055f6e18e08f("block: Make q_usage_counter also track legacy requests",
the q_usage_counter just works for sync IO(such as dax) because we only
hold the refcount when calling q->make_request_fn(), so blk_drain_queue()
does do the job always.
Thanks,
Ming
