Date: Tue, 23 Jul 2013 20:08:54 +0200
From: Michael Leun <lkml20130126@newton.leun.net>
To: Colin Cross <ccross@android.com>
Cc: Michael Leun <lkml20130126@newton.leun.net>,
        lkml <linux-kernel@vger.kernel.org>, Pavel Machek <pavel@ucw.cz>,
        "Rafael J. Wysocki" <rjw@sisk.pl>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mandeep Singh Baines <msb@chromium.org>,
        Oleg Nesterov <oleg@redhat.com>, linux-nfs <linux-nfs@vger.kernel.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tejun Heo <tj@kernel.org>, Darren Hart <dvhart@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Randy Dunlap <rdunlap@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: 3.11-rc regression bisected: s2disk does not work (was Re:
 [PATCH v3 13/16] futex: use freezable blocking call)
Message-ID: <20130723200854.2046296b@xenia.leun.net>
In-Reply-To: <CAMbhsRQv+W897_5qGuNJD47jQ9ozN6KxeCa6UJAvZpqVuBpQ4w@mail.gmail.com>
References: <1367884221-20462-1-git-send-email-ccross@android.com>
	<1367884221-20462-14-git-send-email-ccross@android.com>
	<20130723010250.5a3465ec@xenia.leun.net>
	<CAMbhsRQv+W897_5qGuNJD47jQ9ozN6KxeCa6UJAvZpqVuBpQ4w@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-nfs-owner@vger.kernel.org

On Mon, 22 Jul 2013 16:55:58 -0700
Colin Cross <ccross@android.com> wrote:

> On Mon, Jul 22, 2013 at 4:02 PM, Michael Leun
> <lkml20130126@newton.leun.net> wrote:
> > On Mon,  6 May 2013 16:50:18 -0700
> > Colin Cross <ccross@android.com> wrote:
> >
> >> Avoid waking up every thread sleeping in a futex_wait call during
> > [...]
> >
> > With 3.11-rc s2disk from suspend-utils stopped working: Frozen at
> > displaying 0% of saving image to disk.
> >
> > echo "1" >/sys/power/state still works.
> >
> > Bisecting yielded 88c8004fd3a5fdd2378069de86b90b21110d33a4,
> > reverting that from 3.11-rc2 makes s2disk working again.
> >
> 
> I think the expanded use of the freezable_* helpers is exposing an
> existing bug in hibernation.  The SNAPSHOT_FREEZE ioctl calls
> freeze_processes(), which sets the global system_freezing_cnt and
> pm_freezing.  try_to_freeze_tasks then sends every process except
> current a signal which causes them all to end up in the refrigerator.
> The current task then returns back to userspace and continues its work
> to suspend to disk.  If that task ever hits a call to try_to_freeze()
> in the kernel, it will see system_freezing_cnt and pm_freezing=true
> and freeze, and suspend to disk will hang forever.  It could hit
> try_to_freeze() because of a signal delivered to the task, or from
> calling any syscall that uses a freezable_* helper like the one I
> added to sys_futex.
> 
> I think the right solution is to add a flag to the freezing task that
> marks it unfreezable.  I  think PF_NOFREEZE would work, although it is
> normally used on kernel threads, can you see if the attached patch
> helps?

That patch helps.

BTW, the only machine I can reproduce this bug with is an i7-3630QM
notebook. Cannot reproduce on an Core Duo U1400 and cannot reproduce on
an i7 M 620.

Are the sysreq backtraces still wanted? If so, any tip, how I could get
them saved?


-- 
MfG,

Michael Leun