nbd: fix I/O hang on disconnected nbds
Fix a problem that causes I/O to a disconnected (or partially initialized)
nbd device to hang indefinitely. To reproduce:
# ioctl NBD_SET_SIZE_BLOCKS /dev/nbd23 514048
# dd if=/dev/nbd23 of=/dev/null bs=4096 count=1
...hangs...
This can also occur when an nbd device loses its nbd-client/server
connection. Although we clear the queue of any outstanding I/Os after the
client/server connection fails, any additional I/Os that get queued later
will hang.
This bug may also be the problem reported in this bug report:
http://bugzilla.kernel.org/show_bug.cgi?id=12277
Testing would need to be performed to determine if the two issues are the
same.
This problem was introduced by the new request handling thread code ("NBD:
allow nbd to be used locally", 3/2008), which entered into mainline around
2.6.25.
The fix, which is fairly simple, is to restore the check for lo->sock
being NULL in do_nbd_request. This causes I/O to an uninitialized nbd to
immediately fail with an I/O error, as it did prior to the introduction of
this bug.
Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Reported-by: Jon Nelson <jnelson-kernel-bugzilla@jamponi.net>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: <stable@kernel.org> [2.6.26.x, 2.6.27.x, 2.6.28.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 34f80fa..8299e2d 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -549,6 +549,15 @@
BUG_ON(lo->magic != LO_MAGIC);
+ if (unlikely(!lo->sock)) {
+ printk(KERN_ERR "%s: Attempted send on closed socket\n",
+ lo->disk->disk_name);
+ req->errors++;
+ nbd_end_request(req);
+ spin_lock_irq(q->queue_lock);
+ continue;
+ }
+
spin_lock_irq(&lo->queue_lock);
list_add_tail(&req->queuelist, &lo->waiting_queue);
spin_unlock_irq(&lo->queue_lock);