[ 005/108] nbd: clear waiting_queue on shutdown

Ben Hutchings
2012-10-07T23:22:14Z

From: Paul Clements <paul.clements@steeleye.com>

commit fded4e090c60100d709318896c79816d68d5b47d upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: local nbd_device pointers are called 'lo' not 'nbd']
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/block/nbd.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -445,6 +445,14 @@ static void nbd_clear_que(struct nbd_dev
req->errors++;
nbd_end_request(req);
}
+
+ while (!list_empty(&lo->waiting_queue)) {
+ req = list_entry(lo->waiting_queue.next, struct request,
+ queuelist);
+ list_del_init(&req->queuelist);
+ req->errors++;
+ nbd_end_request(req);
+ }
}

@@ -594,6 +602,7 @@ static int __nbd_ioctl(struct block_devi
lo->file = NULL;
nbd_clear_que(lo);
BUG_ON(!list_empty(&lo->queue_head));
+ BUG_ON(!list_empty(&lo->waiting_queue));
if (file)
fput(file);
return 0;