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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)
    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



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