On 03/24/2017 01:36 PM, Ming Lei wrote: > Without the barrier, reading DEAD flag of .q_usage_counter > and reading .mq_freeze_depth may be reordered, then the > following wait_event_interruptible() may never return. > > Signed-off-by: Ming Lei <tom.leiming@xxxxxxxxx> > --- > block/blk-core.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/block/blk-core.c b/block/blk-core.c > index ad388d5e309a..44eed17319c0 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -669,6 +669,14 @@ int blk_queue_enter(struct request_queue *q, bool nowait) > if (nowait) > return -EBUSY; > > + /* > + * read pair of barrier in blk_mq_freeze_queue_start(), > + * we need to order reading DEAD flag of .q_usage_counter > + * and reading .mq_freeze_depth, otherwise the following > + * wait may never return if the two read are reordered. > + */ > + smp_rmb(); > + > ret = wait_event_interruptible(q->mq_freeze_wq, > !atomic_read(&q->mq_freeze_depth) || > blk_queue_dying(q)); > Reviewed-by: Hannes Reinecke <hare@xxxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
