From f4560ffe8cec1361b1021d81aca6a4173f8e7c87 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Sun, 18 Jun 2017 14:24:27 -0600 Subject: blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue 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. Signed-off-by: Ming Lei Reviewed-by: Bart Van Assche Signed-off-by: Jens Axboe --- block/blk-mq-sched.c | 3 ++- block/blk-mq.c | 11 ++++++++++- 2 files changed, 12 insertions(+), 2 deletions(-) (limited to 'block') diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 254d1c164567..9f025289da63 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -58,7 +58,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx) bool did_work = false; LIST_HEAD(rq_list); - if (unlikely(blk_mq_hctx_stopped(hctx))) + /* RCU or SRCU read lock is needed before checking quiesced flag */ + if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q))) return; hctx->run++; diff --git a/block/blk-mq.c b/block/blk-mq.c index 07785b5cf2bc..40b22c7f684e 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -170,6 +170,10 @@ void blk_mq_quiesce_queue(struct request_queue *q) __blk_mq_stop_hw_queues(q, true); + spin_lock_irq(q->queue_lock); + queue_flag_set(QUEUE_FLAG_QUIESCED, q); + spin_unlock_irq(q->queue_lock); + queue_for_each_hw_ctx(q, hctx, i) { if (hctx->flags & BLK_MQ_F_BLOCKING) synchronize_srcu(&hctx->queue_rq_srcu); @@ -190,6 +194,10 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue); */ void blk_mq_unquiesce_queue(struct request_queue *q) { + spin_lock_irq(q->queue_lock); + queue_flag_clear(QUEUE_FLAG_QUIESCED, q); + spin_unlock_irq(q->queue_lock); + blk_mq_start_stopped_hw_queues(q, true); } EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue); @@ -1444,7 +1452,8 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx, blk_status_t ret; bool run_queue = true; - if (blk_mq_hctx_stopped(hctx)) { + /* RCU or SRCU read lock is needed before checking quiesced flag */ + if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) { run_queue = false; goto insert; } -- cgit