4.16-stable review patch. If anyone has any objections, please let me know.
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From: Bart Van Assche bart.vanassche@wdc.com
commit 818e0fa293ca836eba515615c64680ea916fd7cd upstream.
scsi_device_quiesce() uses synchronize_rcu() to guarantee that the effect of blk_set_preempt_only() will be visible for percpu_ref_tryget() calls that occur after the queue unfreeze by using the approach explained in https://lwn.net/Articles/573497/. The rcu read lock and unlock calls in blk_queue_enter() form a pair with the synchronize_rcu() call in scsi_device_quiesce(). Both scsi_device_quiesce() and blk_queue_enter() must either use regular RCU or RCU-sched. Since neither the RCU-protected code in blk_queue_enter() nor blk_queue_usage_counter_release() sleeps, regular RCU protection is sufficient. Note: scsi_device_quiesce() does not have to be modified since it already uses synchronize_rcu().
Reported-by: Tejun Heo tj@kernel.org Fixes: 3a0a529971ec ("block, scsi: Make SCSI quiesce and resume work reliably") Signed-off-by: Bart Van Assche bart.vanassche@wdc.com Acked-by: Tejun Heo tj@kernel.org Cc: Tejun Heo tj@kernel.org Cc: Hannes Reinecke hare@suse.com Cc: Ming Lei ming.lei@redhat.com Cc: Christoph Hellwig hch@lst.de Cc: Johannes Thumshirn jthumshirn@suse.de Cc: Oleksandr Natalenko oleksandr@natalenko.name Cc: Martin Steigerwald martin@lichtvoll.de Cc: stable@vger.kernel.org # v4.15 Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/block/blk-core.c +++ b/block/blk-core.c @@ -827,7 +827,7 @@ int blk_queue_enter(struct request_queue bool success = false; int ret;
- rcu_read_lock_sched(); + rcu_read_lock(); if (percpu_ref_tryget_live(&q->q_usage_counter)) { /* * The code that sets the PREEMPT_ONLY flag is @@ -840,7 +840,7 @@ int blk_queue_enter(struct request_queue percpu_ref_put(&q->q_usage_counter); } } - rcu_read_unlock_sched(); + rcu_read_unlock();
if (success) return 0;