[PATCH -next] blk-mq: fix potential io hang by wrong 'wake_batch'

[Yu Kuai]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

In __blk_mq_tag_busy/idle(), updating 'active_queues' and calculating
'wake_batch' is not atomic:

t1:			t2:
_blk_mq_tag_busy	blk_mq_tag_busy
inc active_queues
// assume 1->2
			inc active_queues
			// 2 -> 3
			blk_mq_update_wake_batch
			// calculate based on 3
blk_mq_update_wake_batch
/* calculate based on 2, while active_queues is actually 3. */

Fix this problem by protecting them wih 'tags->lock', this is not a hot
path, so performance should not be concerned.

Fixes: 180dccb0dba4 ("blk-mq: fix tag_get wait task can't be awakened")
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-mq-tag.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index dfd81cab5788..43fe523f39c7 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -55,9 +55,10 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 			return;
 	}
 
+	spin_lock_irq(&hctx->tags->lock);
 	users = atomic_inc_return(&hctx->tags->active_queues);
-
 	blk_mq_update_wake_batch(hctx->tags, users);
+	spin_unlock_irq(&hctx->tags->lock);
 }
 
 /*
@@ -90,9 +91,10 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 			return;
 	}
 
+	spin_lock_irq(&tags->lock);
 	users = atomic_dec_return(&tags->active_queues);
-
 	blk_mq_update_wake_batch(tags, users);
+	spin_unlock_irq(&tags->lock);
 
 	blk_mq_tag_wakeup_all(tags, false);
 }
-- 
2.39.2