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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Stefan Roesch <shr@fb.com>,
        Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.15 14/45] block: blk_queue_enter() / __bio_queue_enter() must return -EAGAIN for nowait
Date:   Wed, 21 Sep 2022 17:46:04 +0200
Message-Id: <20220921153647.356578998@linuxfoundation.org>
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From: Stefan Roesch <shr@fb.com>

[ Upstream commit 56f99b8d06ef1ed1c9730948f9f05ac2b930a20b ]

Today blk_queue_enter() and __bio_queue_enter() return -EBUSY for the
nowait code path. This is not correct: they should return -EAGAIN
instead.

This problem was detected by fio. The following command exposed the
above problem:

t/io_uring -p0 -d128 -b4096 -s32 -c32 -F1 -B0 -R0 -X1 -n24 -P1 -u1 -O0 /dev/ng0n1

By applying the patch, the retry case is handled correctly in the slow
path.

Signed-off-by: Stefan Roesch <shr@fb.com>
Fixes: bfd343aa1718 ("blk-mq: don't wait in blk_mq_queue_enter() if __GFP_WAIT isn't set")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 block/blk-core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 5009b9f1c3c9..13e1fca1e923 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -447,7 +447,7 @@ int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
 
 	while (!blk_try_enter_queue(q, pm)) {
 		if (flags & BLK_MQ_REQ_NOWAIT)
-			return -EBUSY;
+			return -EAGAIN;
 
 		/*
 		 * read pair of barrier in blk_freeze_queue_start(), we need to
@@ -478,7 +478,7 @@ static inline int bio_queue_enter(struct bio *bio)
 			if (test_bit(GD_DEAD, &disk->state))
 				goto dead;
 			bio_wouldblock_error(bio);
-			return -EBUSY;
+			return -EAGAIN;
 		}
 
 		/*
-- 
2.35.1