linux-kernel - [PATCH 3.19 20/75] virtio-balloon: do not call blocking ops when !TASK

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Date:	Fri, 10 Apr 2015 15:18:46 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Thomas Huth <thuth@...ux.vnet.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: [PATCH 3.19 20/75] virtio-balloon: do not call blocking ops when !TASK_RUNNING

3.19-stable review patch.  If anyone has any objections, please let me know.

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

From: "Michael S. Tsirkin" <mst@...hat.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@...ux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Tested-by: Thomas Huth <thuth@...ux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@...ibm.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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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