From 3e94d54e83cafd2b562bb6d15bb2f72d76200fb5 Mon Sep 17 00:00:00 2001
From: Tian Lan <tian.lan@twosigma.com>
Date: Mon, 22 May 2023 17:05:55 -0400
Subject: [PATCH] blk-mq: fix race condition in active queue accounting
If multiple CPUs are sharing the same hardware queue, it can
cause leak in the active queue counter tracking when __blk_mq_tag_busy()
is executed simultaneously.
Fixes: ee78ec1077d3 ("blk-mq: blk_mq_tag_busy is no need to return a value")
Signed-off-by: Tian Lan <tian.lan@twosigma.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20230522210555.794134-1-tilan7663@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
block/blk-mq-tag.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index d6af9d431dc63..dfd81cab57888 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -39,16 +39,20 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
{
unsigned int users;
+ /*
+ * calling test_bit() prior to test_and_set_bit() is intentional,
+ * it avoids dirtying the cacheline if the queue is already active.
+ */
if (blk_mq_is_shared_tags(hctx->flags)) {
struct request_queue *q = hctx->queue;
- if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
+ if (test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags) ||
+ test_and_set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
return;
- set_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags);
} else {
- if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+ if (test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) ||
+ test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
return;
- set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state);
}
users = atomic_inc_return(&hctx->tags->active_queues);
--
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