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 18:27:43 +0100 Message-ID: <20150226172743.GA20582@redhat.com> References: <20150225111318.0040536b@oc7435384737.ibm.com> <87y4nllb85.fsf@rustcorp.com.au> <20150226083031.GA24184@redhat.com> <20150226170849.GV21418@twins.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Rusty Russell , Thomas Huth , virtualization@lists.linux-foundation.org, kvm@vger.kernel.org To: Peter Zijlstra Return-path: Received: from mx1.redhat.com ([209.132.183.28]:39093 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753716AbbBZR3P (ORCPT ); Thu, 26 Feb 2015 12:29:15 -0500 Content-Disposition: inline In-Reply-To: <20150226170849.GV21418@twins.programming.kicks-ass.net> Sender: kvm-owner@vger.kernel.org List-ID: 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 ----- End forwarded message -----