nbd: clear waiting_queue on shutdown

Fix a serious but uncommon bug in nbd which occurs when there is heavy
I/O going to the nbd device while, at the same time, a failure (server,
network) or manual disconnect of the nbd connection occurs.

There is a small window between the time that the nbd_thread is stopped
and the socket is shutdown where requests can continue to be queued to
nbd's internal waiting_queue.  When this happens, those requests are
never completed or freed.

The fix is to clear the waiting_queue on shutdown of the nbd device, in
the same way that the nbd request queue (queue_head) is already being
cleared.

Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index d07c9f7fded6..0c03411c59eb 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -449,6 +449,14 @@ static void nbd_clear_que(struct nbd_device *nbd)
                 req->errors++;
                 nbd_end_request(req);
         }
+
+        while (!list_empty(&nbd->waiting_queue)) {
+                req = list_entry(nbd->waiting_queue.next, struct request,
+                                 queuelist);
+                list_del_init(&req->queuelist);
+                req->errors++;
+                nbd_end_request(req);
+        }
 }
 
 
@@ -598,6 +606,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
                 nbd->file = NULL;
                 nbd_clear_que(nbd);
                 BUG_ON(!list_empty(&nbd->queue_head));
+                BUG_ON(!list_empty(&nbd->waiting_queue));
                 if (file)
                         fput(file);
                 return 0;