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    SubjectRe: [RFC] Cpu-hotplug: Using the Process Freezer (try2)
    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.

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

    I will rerun my tests with this hunk applied and report back.

    >
    > Ingo

    Thanks and Regards
    gautham.
    --
    Gautham R Shenoy
    Linux Technology Center
    IBM India.
    "Freedom comes with a price tag of responsibility, which is still a bargain,
    because Freedom is priceless!"
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