From 4d48a542b42747c36a5937447d9c3de7c897ea50 Mon Sep 17 00:00:00 2001 From: Paul Clements Date: Wed, 11 Feb 2009 13:04:45 -0800 Subject: [PATCH] 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 Reported-by: Jon Nelson Acked-by: Pavel Machek Cc: [2.6.26.x, 2.6.27.x, 2.6.28.x] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/nbd.c | 9 +++++++++ 1 file changed, 9 insertions(+) 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 @@ static void do_nbd_request(struct request_queue * q) 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); -- 2.7.4