virtio-balloon: do not call blocking ops when !TASK_RUNNING

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@vger.kernel.org
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>

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index b36fe56677d5e2fb3f6d790985f79802adccbc4a..6a356e344f82c3d5b594abeeb47c453e868c4f9f 100644 (file)
--- 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
@@ -334,17 +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();
-               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)