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SubjectRe: 3.11-rc regression bisected: s2disk does not work (was Re: [PATCH v3 13/16] futex: use freezable blocking call)
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On Tue, Jul 23, 2013 at 11:08 AM, Michael Leun
<lkml20130126@newton.leun.net> wrote:
> 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
>

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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