On Thu, Feb 26, 2015 at 06:08:49PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 26, 2015 at 09:30:31AM +0100, Michael S. Tsirkin wrote:
> > On Thu, Feb 26, 2015 at 11:50:42AM +1030, Rusty Russell wrote:
> > > Thomas Huth <th...@linux.vnet.ibm.com> writes:
> > > > Hi all,
> > > >
> > > > with the recent kernel 3.19, I get a kernel warning when I start my
> > > > KVM guest on s390 with virtio balloon enabled:
> > >
> > > The deeper problem is that virtio_ccw_get_config just silently fails on
> > > OOM.
> > >
> > > Neither get_config nor set_config are expected to fail.
> > >
> > > Cornelia, I think ccw and config_area should be allocated inside vcdev.
> > > You could either use pointers, or simply allocate vcdev with GDP_DMA.
> > >
> > > This would avoid the kmalloc inside these calls.
> > >
> > > Thanks,
> > > Rusty.
> >
> > But it won't solve the problem of nested sleepers
> > with ccw: ATM is invokes ccw_io_helper to execute
> > commands, and that one calls wait_event
> > to wait for an interrupt.
> >
> > Might be fixable but I think my patch looks like a safer
> > solution for 4.0/3.19, no?
>
> I've no idea what your patch was since I'm not subscribed to any of the
> lists this discussion is had on.
Oh, sorry about that.
Here it is, below:
----- Forwarded message from "Michael S. Tsirkin" <m...@redhat.com> -----
Date: Wed, 25 Feb 2015 15:36:02 +0100
From: "Michael S. Tsirkin" <m...@redhat.com>
To: linux-ker...@vger.kernel.org
Cc: sta...@vger.kernel.org, Thomas Huth <th...@linux.vnet.ibm.com>, Rusty
Russell <ru...@rustcorp.com.au>,
virtualizat...@lists.linux-foundation.org, kvm@vger.kernel.org,
Cornelia Huck <cornelia.h...@de.ibm.com>
Subject: [PATCH v2] virtio-balloon: do not call blocking ops when !TASK_RUNNING
Message-ID: <1424874878-17155-1-git-send-email-...@redhat.com>
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: sta...@vger.kernel.org
Reported-by: Thomas Huth <th...@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
changes from v1:
remove wait_event_interruptible
noticed by Cornelia Huck <cornelia.h...@de.ibm.com>
drivers/virtio/virtio_balloon.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 0413157..5a6ad6d 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
@@ -334,17 +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)
--
MST
----- End forwarded message -----
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