linux-kernel - [PATCH block/for-6.2-fixes] block: Drop spurious might_sleep() from blk_put

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Date:   Fri, 6 Jan 2023 10:34:10 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Dan Carpenter <error27@...il.com>, Christoph Hellwig <hch@....de>,
        Luis Chamberlain <mcgrof@...nel.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH block/for-6.2-fixes] block: Drop spurious might_sleep() from
 blk_put_queue()

Dan reports the following smatch detected the following:

  block/blk-cgroup.c:1863 blkcg_schedule_throttle() warn: sleeping in atomic context

caused by blkcg_schedule_throttle() calling blk_put_queue() in an
non-sleepable context.

blk_put_queue() acquired might_sleep() in 63f93fd6fa57 ("block: mark
blk_put_queue as potentially blocking") which transferred the might_sleep()
from blk_free_queue().

blk_free_queue() acquired might_sleep() in e8c7d14ac6c3 ("block: revert back
to synchronous request_queue removal") while turning request_queue removal
synchronous. However, this isn't necessary as nothing in the free path
actually requires sleeping.

It's pretty unusual to require a sleeping context in a put operation and
it's not needed in the first place. Let's drop it.

Signed-off-by: Tejun Heo <tj@...nel.org>
Reported-by: Dan Carpenter <error27@...il.com>
Link: https://lkml.kernel.org/r/Y7g3L6fntnTtOm63@kili
Cc: Christoph Hellwig <hch@....de>
Cc: Luis Chamberlain <mcgrof@...nel.org>
Fixes: e8c7d14ac6c3 ("block: revert back to synchronous request_queue removal") # v5.9+
--
 block/blk-core.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 9321767470dc..b5098355d8b2 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -283,12 +283,9 @@ static void blk_free_queue(struct request_queue *q)
  *
  * Decrements the refcount of the request_queue and free it when the refcount
  * reaches 0.
- *
- * Context: Can sleep.
  */
 void blk_put_queue(struct request_queue *q)
 {
-	might_sleep();
 	if (refcount_dec_and_test(&q->refs))
 		blk_free_queue(q);
 }