From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: virtio balloon: do not call blocking ops when !TASK_RUNNING Date: Thu, 26 Feb 2015 18:41:19 +0100 Message-ID: <20150226174119.GA20674@redhat.com> References: <20150225111318.0040536b@oc7435384737.ibm.com> <87y4nllb85.fsf@rustcorp.com.au> <20150226083031.GA24184@redhat.com> <20150226170849.GV21418@twins.programming.kicks-ass.net> <20150226172743.GA20582@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20150226172743.GA20582@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Peter Zijlstra Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org List-Id: virtualization@lists.linuxfoundation.org On Thu, Feb 26, 2015 at 06:27:43PM +0100, Michael S. Tsirkin wrote: > 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 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" ----- > > Date: Wed, 25 Feb 2015 15:36:02 +0100 > From: "Michael S. Tsirkin" > To: linux-kernel@vger.kernel.org > Cc: stable@vger.kernel.org, Thomas Huth , Rusty Russell , > virtualization@lists.linux-foundation.org, kvm@vger.kernel.org, Cornelia Huck > Subject: [PATCH v2] virtio-balloon: do not call blocking ops when !TASK_RUNNING > Message-ID: <1424874878-17155-1-git-send-email-mst@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: stable@vger.kernel.org > Reported-by: Thomas Huth > Signed-off-by: Michael S. Tsirkin > --- > > changes from v1: > remove wait_event_interruptible > noticed by Cornelia Huck > > 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 > #include > #include > +#include > > /* > * 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 WRT which, I have a question. IIUC it's OK for towards_target in this code to call wait_event in its turn, assuming that *that* wait_event is not not calling blocking ops. Right? > ----- End forwarded message -----