[Nbd] [PATCH] nbd: remove false assertion

[Michal Belczyk <belczyk@...1274...>]

This case can be easily reproduced with the following steps:

*) launch nbd-client with a timeout value specified:

   nbd-client 127.0.0.1 /dev/nbd0 -block-size 4096 -name vol0 -timeout 10

*) block nbd traffic:

   iptables -I OUTPUT -p tcp --dport 10809 -j DROP
   iptables -I INPUT -p tcp --sport 10809 -j DROP

*) issue a large write request to make nbd sender thread block
   in kernel_sendmsg() and cause the timeout to kick in:

   dd if=/dev/zero of=/dev/nbd0 bs=8M oflag=direct

*) before the timeout occurs run nbd-client -d /dev/nbd0 in another terminal
   and watch the effects (see dmesg)

What happens here is that nbd-client -d thread is waiting to acquire tx_lock
which is acquired by the nbd sender thread (nbd_thread) but once the request
fails the socket is shut down via sock_shutdown() (called from sock_xmit(),
nbd->sock == NULL after this happens), later back in nbd_handle_req() the
mutex is released, nbd-client -d enters __nbd_ioctl(NBD_CLEAR_QUE) code and
the assertion is triggered as there are more requests waiting to be sent...

Signed-off-by: Michal Belczyk <belczyk@...1274...>
---
 drivers/block/nbd.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 037288e..c09640a 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -746,11 +746,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 	}
 
 	case NBD_CLEAR_QUE:
-		/*
-		 * This is for compatibility only.  The queue is always cleared
-		 * by NBD_DO_IT or NBD_CLEAR_SOCK.
-		 */
-		BUG_ON(!nbd->sock && !list_empty(&nbd->queue_head));
+		/* This is for compatibility only */
 		return 0;
 
 	case NBD_PRINT_DEBUG:
-- 
1.8.1.4


-- 
Michal Belczyk Sr.