linux-kernel - [PATCH 5.9 179/391] nbd: make the config put is called before the notifying the waiter

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Date:   Tue,  3 Nov 2020 21:33:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiubo Li <xiubli@...hat.com>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.9 179/391] nbd: make the config put is called before the notifying the waiter

From: Xiubo Li <xiubli@...hat.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@...hat.com>
Reviewed-by: Josef Bacik <josef@...icpanda.com>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.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 edf8b632e3d27..f46e26c9d9b3c 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -801,9 +801,9 @@ static void recv_work(struct work_struct *work)
 		if (likely(!blk_should_fake_timeout(rq->q)))
 			blk_mq_complete_request(rq);
 	}
+	nbd_config_put(nbd);
 	atomic_dec(&config->recv_threads);
 	wake_up(&config->recv_wq);
-	nbd_config_put(nbd);
 	kfree(args);
 }
 
-- 
2.27.0