virtio balloon has this code:
wait_event_interruptible(vb->config_change,
(diff = towards_target(vb)) != 0
|| vb->need_stats_update
|| kthread_should_stop()
|| freezing(current));
Which is a problem because towards_target() call might block after
wait_event_interruptible sets task state to TAST_INTERRUPTIBLE, causing
the task_struct::state collision typical of nesting of sleeping
primitives
See also http://lwn.net/Articles/628628/ or Thomas's
bug report
http://article.gmane.org/gmane.linux.kernel.virtualization/24846
for a fuller explanation.
To fix, rewrite using wait_woken.
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Thomas Huth <thuth@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
drivers/virtio/virtio_balloon.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 0413157..2f19f65 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -29,6 +29,7 @@
#include <linux/module.h>
#include <linux/balloon_compaction.h>
#include <linux/oom.h>
+#include <linux/wait.h>
/*
* Balloon device works in 4K page units. So each page is pointed to by
@@ -334,12 +335,25 @@ static int virtballoon_oom_notify(struct notifier_block *self,
static int balloon(void *_vballoon)
{
struct virtio_balloon *vb = _vballoon;
+ DEFINE_WAIT_FUNC(wait, woken_wake_function);
set_freezable();
while (!kthread_should_stop()) {
s64 diff;
try_to_freeze();
+
+ add_wait_queue(&vb->config_change, &wait);
+ for (;;) {
+ if ((diff = towards_target(vb)) != 0 ||
+ vb->need_stats_update ||
+ kthread_should_stop() ||
+ freezing(current))
+ break;
+ wait_woken(&wait, TASK_INTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
+ }
+ remove_wait_queue(&vb->config_change, &wait);
+
wait_event_interruptible(vb->config_change,
(diff = towards_target(vb)) != 0
|| vb->need_stats_update
--
MST
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