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

[Michael Leun <lkml20130126@newton.leun.net>]

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