[3.13.y.z extended stable] Patch "virtio_balloon: don't softlockup on huge balloon changes." has been added to staging queue

Kamal Mostafa kamal at canonical.com
Thu May 1 19:17:12 UTC 2014

This is a note to let you know that I have just added a patch titled

    virtio_balloon: don't softlockup on huge balloon changes.

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see



>From 02753a2dae83d52329b6cbfbcbffc14607e05931 Mon Sep 17 00:00:00 2001
From: Rusty Russell <rusty at rustcorp.com.au>
Date: Thu, 13 Mar 2014 11:23:38 +1030
Subject: virtio_balloon: don't softlockup on huge balloon changes.

commit 1f74ef0f2d7d692fcd615621e0e734c3e7771413 upstream.

When adding or removing 100G from a balloon:

    BUG: soft lockup - CPU#0 stuck for 22s! [vballoon:367]

We have a wait_event_interruptible(), but the condition is always true
(more ballooning to do) so we don't ever sleep.  We also have a
wait_event() for the host to ack, but that is also always true as QEMU
is synchronous for balloon operations.

Reported-by: Gopesh Kumar Chaudhary <gopchaud at in.ibm.com>
Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 drivers/virtio/virtio_balloon.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 5c4a95b..5f8af50 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -310,6 +310,12 @@ static int balloon(void *_vballoon)
 		else if (diff < 0)
 			leak_balloon(vb, -diff);
+		/*
+		 * For large balloon changes, we could spend a lot of time
+		 * and always have work to do.  Be nice if preempt disabled.
+		 */
+		cond_resched();
 	return 0;

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