On Tue, 2017-06-06 at 23:22 +0800, Ming Lei wrote: > It is required that no dispatch can happen any more once > blk_mq_quiesce_queue() returns, and we don't have such requirement > on APIs of stopping queue. > > But blk_mq_quiesce_queue() still may not block/drain dispatch in the > the case of BLK_MQ_S_START_ON_RUN, so use the new introduced flag of > QUEUE_FLAG_QUIESCED and evaluate it inside RCU read-side critical > sections for fixing this issue. > > Also blk_mq_quiesce_queue() is implemented via stopping queue, which > limits its uses, and easy to cause race, because any queue restart in > other paths may break blk_mq_quiesce_queue(). With the introduced > flag of QUEUE_FLAG_QUIESCED, we don't need to depend on stopping queue > for quiescing any more. Reviewed-by: Bart Van Assche <Bart.VanAssche@xxxxxxxxxxx>
