4.16-stable review patch. If anyone has any objections, please let me know.
------------------ From: Bart Van Assche <bart.vanass...@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 <t...@kernel.org> Fixes: 3a0a529971ec ("block, scsi: Make SCSI quiesce and resume work reliably") Signed-off-by: Bart Van Assche <bart.vanass...@wdc.com> Acked-by: Tejun Heo <t...@kernel.org> Cc: Tejun Heo <t...@kernel.org> Cc: Hannes Reinecke <h...@suse.com> Cc: Ming Lei <ming....@redhat.com> Cc: Christoph Hellwig <h...@lst.de> Cc: Johannes Thumshirn <jthumsh...@suse.de> Cc: Oleksandr Natalenko <oleksa...@natalenko.name> Cc: Martin Steigerwald <mar...@lichtvoll.de> Cc: sta...@vger.kernel.org # v4.15 Signed-off-by: Jens Axboe <ax...@kernel.dk> Signed-off-by: Greg Kroah-Hartman <gre...@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;
