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Commit 3d2a3774 authored by Michael S. Tsirkin's avatar Michael S. Tsirkin Committed by Rusty Russell
Browse files

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: default avatarThomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Tested-by: default avatarThomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: default avatarCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 0fa2a564

drivers/virtio/virtio_balloon.c

+14 −5
Original line number Diff line number Diff line
@@ -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)