[PATCH 2/9] dm: Fix a race condition related to stopping and starting queues
From: Bart Van Assche <hidden>
Date: 2016-09-26 18:27:00
Also in:
linux-nvme, linux-rdma, linux-scsi
Subsystem:
device-mapper (lvm), the rest · Maintainers:
Alasdair Kergon, Mike Snitzer, Mikulas Patocka, Benjamin Marzinski, Linus Torvalds
Ensure that all ongoing dm_mq_queue_rq() and dm_mq_requeue_request() calls have stopped before setting the "queue stopped" flag. This allows to remove the "queue stopped" test from dm_mq_queue_rq() and dm_mq_requeue_request(). This patch fixes a race condition because dm_mq_queue_rq() is called without holding the queue lock and hence BLK_MQ_S_STOPPED can be set at any time while dm_mq_queue_rq() is in progress. Signed-off-by: Bart Van Assche <redacted> Cc: Mike Snitzer <redacted> --- drivers/md/dm-rq.c | 14 +++----------- 1 file changed, 3 insertions(+), 11 deletions(-)
diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 182b679..1b7a65e 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c@@ -116,9 +116,12 @@ static void dm_mq_stop_queue(struct request_queue *q) queue_flag_set(QUEUE_FLAG_STOPPED, q); spin_unlock_irqrestore(q->queue_lock, flags); + /* Wait until dm_mq_queue_rq() has finished. */ + blk_quiesce_queue(q); /* Avoid that requeuing could restart the queue. */ blk_mq_cancel_requeue_work(q); blk_mq_stop_hw_queues(q); + blk_resume_queue(q); } void dm_stop_queue(struct request_queue *q)
@@ -901,17 +904,6 @@ static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx, dm_put_live_table(md, srcu_idx); } - /* - * On suspend dm_stop_queue() handles stopping the blk-mq - * request_queue BUT: even though the hw_queues are marked - * BLK_MQ_S_STOPPED at that point there is still a race that - * is allowing block/blk-mq.c to call ->queue_rq against a - * hctx that it really shouldn't. The following check guards - * against this rarity (albeit _not_ race-free). - */ - if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state))) - return BLK_MQ_RQ_QUEUE_BUSY; - if (ti->type->busy && ti->type->busy(ti)) return BLK_MQ_RQ_QUEUE_BUSY;
--
2.10.0