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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Xiubo Li <xiubli@redhat.com>, Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>, Sasha Levin <sashal@kernel.org>,
        linux-block@vger.kernel.org, nbd@other.debian.org
Subject: [PATCH AUTOSEL 5.4 78/80] nbd: make the config put is called before the notifying the waiter
Date:   Mon, 26 Oct 2020 19:55:14 -0400
Message-Id: <20201026235516.1025100-78-sashal@kernel.org>
In-Reply-To: <20201026235516.1025100-1-sashal@kernel.org>
References: <20201026235516.1025100-1-sashal@kernel.org>
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From: Xiubo Li <xiubli@redhat.com>

[ Upstream commit 87aac3a80af5cbad93e63250e8a1e19095ba0d30 ]

There has one race case for ceph's rbd-nbd tool. When do mapping
it may fail with EBUSY from ioctl(nbd, NBD_DO_IT), but actually
the nbd device has already unmaped.

It dues to if just after the wake_up(), the recv_work() is scheduled
out and defers calling the nbd_config_put(), though the map process
has exited the "nbd->recv_task" is not cleared.

Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/block/nbd.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 7c577cabb9c3b..742f8160b6e28 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -787,9 +787,9 @@ static void recv_work(struct work_struct *work)
 
 		blk_mq_complete_request(blk_mq_rq_from_pdu(cmd));
 	}
+	nbd_config_put(nbd);
 	atomic_dec(&config->recv_threads);
 	wake_up(&config->recv_wq);
-	nbd_config_put(nbd);
 	kfree(args);
 }
 
-- 
2.25.1