[PATCH 3.4 05/22] virtio_balloon: dont softlockup on huge balloon changes.

Greg Kroah-Hartman
2014-05-11T19:31:51Z

From: Rusty Russell <rusty@rustcorp.com.au>

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@in.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/virtio/virtio_balloon.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -305,6 +305,12 @@ static int balloon(void *_vballoon)
else if (diff < 0)
leak_balloon(vb, -diff);
update_balloon_size(vb);
+
+ /*
+ * 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;
}