linux-kernel - Re: 3.11-rc regression bisected: s2disk does not work (was Re: [PATCH v3 13/16] futex: use freezable blocking call)

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Date:	Tue, 23 Jul 2013 11:29:57 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Michael Leun <lkml20130126@...ton.leun.net>
Cc:	lkml <linux-kernel@...r.kernel.org>, Pavel Machek <pavel@....cz>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	linux-nfs <linux-nfs@...r.kernel.org>,
	Linux PM list <linux-pm@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	Al Viro <viro@...iv.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)

On Tue, Jul 23, 2013 at 11:08 AM, Michael Leun
<lkml20130126@...ton.leun.net> wrote:
> On Mon, 22 Jul 2013 16:55:58 -0700
> Colin Cross <ccross@...roid.com> wrote:
>
>> On Mon, Jul 22, 2013 at 4:02 PM, Michael Leun
>> <lkml20130126@...ton.leun.net> wrote:
>> > On Mon,  6 May 2013 16:50:18 -0700
>> > Colin Cross <ccross@...roid.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
>

Any chance that the failing machine has threads=y in the suspend.conf file?

Rafael, it appears that swsusp's suspend.c spawns new threads after
calling the SNAPSHOT_FREEZE ioctl.  The PF_NOFREEZE (or the new flag)
will get copied to those new threads, but nothing will clear the flag.
 Should I just assume that the userspace suspend code will kill those
threads before continuing with suspend?  Or maybe add a WARN_ON in the
kernel if any threads besides current have the new flag set when the
suspend ops that assume all of userspace is frozen are called?
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