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    SubjectRe: [RFC] Cpu-hotplug: Using the Process Freezer (try2)
    Date
    On Tuesday, 3 April 2007 14:01, Gautham R Shenoy wrote:
    > On Mon, Apr 02, 2007 at 08:16:12AM +0200, Ingo Molnar wrote:
    > >
    > > i'm wondering about how TASK_UNINTERRUPTIBLE tasks are handled by the
    > > freezer: are they assumed frozen immediately, or do we wait until they
    > > notice their PF_FREEZING and go into try_to_freeze()? I'd expect
    > > TASK_UNINTERRUPTIBLE to be the largest source of latency. (and hence be
    > > the primary source for freezing 'failures')
    >
    > Ok, we might be in some luck. I panic()ed on freezer fail and checked
    > the stacktrace of the unfrozen tasks. The stacktrace of each one looks
    > like:
    > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    > PID: 7697 TASK: cc354a70 CPU: 7 COMMAND: "make"
    > #0 [cc37fe50] schedule at c0431752
    > #1 [cc37fec4] wait_for_completion at c04318d0
    > #2 [cc37ff24] do_fork at c01249a6
    > #3 [cc37ff94] sys_vfork at c0103c1f
    > #4 [cc37ffb4] system_call at c0104d8d
    > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    >
    > Rafael had sent out a patch to fix the vfork race, which can be found at
    > http://lkml.org/lkml/2007/3/1/212
    >
    > However, the hunk
    >
    > @@ -1393,7 +1394,9 @@ long do_fork(unsigned long clone_flags,
    > tracehook_report_clone_complete(clone_flags, nr, p);
    >
    > if (clone_flags & CLONE_VFORK) {
    > + freezer_do_not_count();
    > wait_for_completion(&vfork);
    > + freezer_count();
    > tracehook_report_vfork_done(p, nr);
    > }
    > } else {
    >
    > Seems to be missing in the latest -mm's.

    Good catch!

    > Rafael / Andrew,
    > Any reasons for leaving this hunk out?

    No, absolutely not. It's needed.

    Moreover, freezer-fix-vfork-problem.patch from the broken-out -rc5-mm3
    contains it, so some other patch must have reverted this change.

    [looks]

    Ah, it's utrace-prep-2.patch . Andrew?
    -
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