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Michael S. Tsirkin

2015-Feb-25 14:14 UTC

[PATCH] 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 at vger.kernel.org
Reported-by: Thomas Huth <thuth at linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst at 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
-- 
MST

Cornelia Huck

2015-Feb-25 14:32 UTC

head link

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

On Wed, 25 Feb 2015 15:14:36 +0100
"Michael S. Tsirkin" <mst at 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 at vger.kernel.org
> Reported-by: Thomas Huth <thuth at linux.vnet.ibm.com>
> Signed-off-by: Michael S. Tsirkin <mst at 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()?

Michael S. Tsirkin

2015-Feb-25 14:33 UTC

head link

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

On Wed, Feb 25, 2015 at 03:32:08PM +0100, Cornelia Huck
wrote:> On Wed, 25 Feb 2015 15:14:36 +0100
> "Michael S. Tsirkin" <mst at 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 at vger.kernel.org
> > Reported-by: Thomas Huth <thuth at linux.vnet.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <mst at 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()?
Ugh. Forgot to commit :(
Will resend.

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