On Sat, 2017-03-18 at 02:32 +0800, Ming Lei wrote:

On Sat, Mar 18, 2017 at 1:32 AM, Bart Van Assche wrote:

quoted

+       /*
+        * Avoid that the updates of the queue flags and q_usage_counte=

r

quoted

+        * are reordered.
+        */
+       smp_wmb();

=20
atomic_inc_return() in blk_mq_freeze_queue_start() does imply a
barrier(smp_mb()).

Hello Ming,

It's probably a good idea to mention that in a comment. The implementation
of blk_mq_freeze_queue_start() namely could be changed in the future such
that it uses another atomic operation that doesn't implicitly perform smp_m=
b().

Thanks,

Bart.=