On Mon, 2017-03-27 at 20:06 +0800, Ming Lei wrote: > Before commit 780db2071a(blk-mq: decouble blk-mq freezing > from generic bypassing), the dying flag is checked before > entering queue, and Tejun converts the checking into .mq_freeze_depth, > and assumes the counter is increased just after dying flag > is set. Unfortunately we doesn't do that in blk_set_queue_dying(). > > This patch calls blk_freeze_queue_start() in blk_set_queue_dying(), > so that we can block new I/O coming once the queue is set as dying. > > Given blk_set_queue_dying() is always called in remove path > of block device, and queue will be cleaned up later, we don't > need to worry about undoing the counter. > > Cc: Bart Van Assche <[email protected]> > Cc: Tejun Heo <[email protected]> > Reviewed-by: Hannes Reinecke <[email protected]> > Signed-off-by: Ming Lei <[email protected]> > --- > block/blk-core.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > > diff --git a/block/blk-core.c b/block/blk-core.c > index 60f364e1d36b..e22c4ea002ec 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -500,6 +500,13 @@ void blk_set_queue_dying(struct request_queue *q) > queue_flag_set(QUEUE_FLAG_DYING, q); > spin_unlock_irq(q->queue_lock); > > + /* > + * When queue DYING flag is set, we need to block new req > + * entering queue, so we call blk_freeze_queue_start() to > + * prevent I/O from crossing blk_queue_enter(). > + */ > + blk_freeze_queue_start(q); > > if (q->mq_ops) > blk_mq_wake_waiters(q); > else { > @@ -672,9 +679,9 @@ int blk_queue_enter(struct request_queue *q, bool nowait) > /* > * read pair of barrier in blk_freeze_queue_start(), > * we need to order reading __PERCPU_REF_DEAD flag of > - * .q_usage_counter and reading .mq_freeze_depth, > - * otherwise the following wait may never return if the > - * two reads are reordered. > + * .q_usage_counter and reading .mq_freeze_depth or > + * queue dying flag, otherwise the following wait may > + * never return if the two reads are reordered. > */ > smp_rmb(); >
An explanation of why that crossing can happen is still missing above the blk_freeze_queue_start() call. Additionally, I'm still wondering whether or not we need "Cc: stable" tags for the patches in this series. But since the code looks fine: Reviewed-by: Bart Van Assche <[email protected]> >
