From 87aac3a80af5cbad93e63250e8a1e19095ba0d30 Mon Sep 17 00:00:00 2001
From: Xiubo Li <xiubli@redhat.com>
Date: Tue, 13 Oct 2020 22:45:14 -0400
Subject: [PATCH] nbd: make the config put is called before the notifying the
 waiter
Git-commit: 87aac3a80af5cbad93e63250e8a1e19095ba0d30
Patch-mainline: v5.10-rc1
References: git-fixes

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.

(Coly Li: refreshed for Linux v4.12 based SUSE kernel)

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: Coly Li <colyli@suse.de>

---
 drivers/block/nbd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -741,9 +741,9 @@ static void recv_work(struct work_struct
 
 		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);
 }