From: Xiubo Li <xiubli@redhat.com>
Date: Wed, 14 Oct 2020 02:45:14 +0000 (-0400)
Subject: nbd: make the config put is called before the notifying the waiter
X-Git-Tag: v4.14.204~67
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=0a4e383fc3aa6540f804c4fd1184a96ae5de6ef8;p=users%2Fdwmw2%2Flinux.git

nbd: make the config put is called before the notifying the waiter

[ 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>
---

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index f22fad977c913..cdf62fb94fb15 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -725,9 +725,9 @@ 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);
 }