Re: [PATCH] virtio-balloon: do not call blocking ops when !TASK_RUNNING

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Wed, 25 Feb 2015 15:14:36 +0100
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> 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>
> ---
>  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

Forgot to remove the wait_event_interruptible()?