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    SubjectRe: [PATCH] softlockup: fix problem with long kernel pauses from kgdb
    Peter Zijlstra wrote:
    > On Mon, 2009-07-27 at 15:03 -0500, Jason Wessel wrote:
    >
    >> The fix is to simply invoke sched_clock_tick() to update "cpu sched
    >> clock" on exit from kgdb_handle_exception.
    >>
    >
    > Is that a regular IRQ context, or is that NMI context?
    >
    >

    The patch text there is incorrect (which I can fix), because there were
    3 other versions of this particular patch. The version of this patch
    that tried to use sched_clock_tick() from the exception context hung the
    system because there was lock contention for CPUs that were not in the
    running state.

    In this version, the sched_clock_tick() added in the softlockup_tick(),
    which did not result in a hard hang. I am pretty sure that
    softlockup_tick() runs as a part of the timer interrupt processing from
    run_local_timers(), so there was no further need to turn off the interrupts.

    Jason.

    >> Signed-off-by: Dongdong Deng <Dongdong.Deng@windriver.com>
    >> Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
    >> Cc: Ingo Molnar <mingo@elte.hu>
    >> Cc: peterz@infradead.org
    >> ---
    >> kernel/softlockup.c | 3 +++
    >> 1 file changed, 3 insertions(+)
    >>
    >> --- a/kernel/softlockup.c
    >> +++ b/kernel/softlockup.c
    >> @@ -118,6 +118,9 @@ void softlockup_tick(void)
    >> }
    >>
    >> if (touch_timestamp == 0) {
    >> + /* If the time stamp was touched externally make sure the
    >> + * scheduler tick is up to date as well */
    >> + sched_clock_tick();
    >> __touch_softlockup_watchdog();
    >> return;
    >> }
    >>
    >>
    >
    > Aside from the funny comment style (please fix) the fix does look
    > sensible.
    >

    No problem.

    Thanks,
    Jason.


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