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Subject[PATCH 3.19 20/75] virtio-balloon: do not call blocking ops when !TASK_RUNNING
Date
3.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Michael S. Tsirkin" <mst@redhat.com>

commit 3d2a3774c1b046f548ebea0391a602fd5685a307 upstream.

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.

Reported-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.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 | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)

--- 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
@@ -335,17 +336,25 @@ static int virtballoon_oom_notify(struct
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();
- wait_event_interruptible(vb->config_change,
- (diff = towards_target(vb)) != 0
- || vb->need_stats_update
- || kthread_should_stop()
- || freezing(current));
+
+ 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);
+
if (vb->need_stats_update)
stats_handle_request(vb);
if (diff > 0)



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