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    SubjectRe: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog
    On Thu, Aug 19, 2010 at 10:57:49PM -0400, Don Zickus wrote:
    > On Wed, Aug 18, 2010 at 01:01:56PM -0700, Andrew Morton wrote:
    > > The surprise new requirement that touch_nmi_watchdog() be called from
    > > non-preemptible code does seem to make sense IMO. It's hard to see why
    > > anyone would be touching the watchdog unless he's spinning in irqs-off
    > > code. Except, of course, when we have a utility function which can be
    > > called from wither irqs-on or irqs-off: acpi_os_stall().
    > >
    > > That being said, it's not good to introduce new API requirements by
    > > accident! An audit of all callers should first be performed, at least.
    > >
    > >
    > > The surprise new requirement that touch_softlockup_watchdog() be called
    > > from non-preemptible code doesn't make sense IMO. If I have a piece of
    > > code in the kernel which I expect to sit in TASK_UNINTERRUPTIBLE state
    > > for three minutes waiting for my egg to boil, I should be able to do
    > > that and I should be able to touch the softlockup detector without
    > > needing to go non-preemptible.
    >
    > Ok, so here is my patch that syncs the touch_*_watchdog back in line with
    > the old semantics. Hopefully this will undo any harm I caused.
    >
    > ------------cut -->---------------------------
    >
    > >From b372e821c804982438db090db6b4a2f753c78091 Mon Sep 17 00:00:00 2001
    > From: Don Zickus <dzickus@redhat.com>
    > Date: Thu, 19 Aug 2010 22:48:26 -0400
    > Subject: [PATCH] [lockup detector] sync touch_*_watchdog back to old semantics
    >
    > During my rewrite, the semantics of touch_nmi_watchdog and
    > touch_softlockup_watchdog changed enough to break some drivers
    > (mostly over preemptable regions).
    >
    > This change brings those touch_*_watchdog functions back in line
    > to how they used to work.

    This one looks good to me.
    Thank you Don.

    -Yong

    >
    > Signed-off-by: Don Zickus <dzickus@redhat.com>
    > ---
    > kernel/watchdog.c | 17 ++++++++++++-----
    > 1 files changed, 12 insertions(+), 5 deletions(-)
    >
    > diff --git a/kernel/watchdog.c b/kernel/watchdog.c
    > index 613bc1f..99e35a2 100644
    > --- a/kernel/watchdog.c
    > +++ b/kernel/watchdog.c
    > @@ -122,7 +122,7 @@ static void __touch_watchdog(void)
    >
    > void touch_softlockup_watchdog(void)
    > {
    > - __get_cpu_var(watchdog_touch_ts) = 0;
    > + __raw_get_cpu_var(watchdog_touch_ts) = 0;
    > }
    > EXPORT_SYMBOL(touch_softlockup_watchdog);
    >
    > @@ -142,7 +142,14 @@ void touch_all_softlockup_watchdogs(void)
    > #ifdef CONFIG_HARDLOCKUP_DETECTOR
    > void touch_nmi_watchdog(void)
    > {
    > - __get_cpu_var(watchdog_nmi_touch) = true;
    > + if (watchdog_enabled) {
    > + unsigned cpu;
    > +
    > + for_each_present_cpu(cpu) {
    > + if (per_cpu(watchdog_nmi_touch, cpu) != true)
    > + per_cpu(watchdog_nmi_touch, cpu) = true;
    > + }
    > + }
    > touch_softlockup_watchdog();
    > }
    > EXPORT_SYMBOL(touch_nmi_watchdog);
    > @@ -430,6 +437,9 @@ static int watchdog_enable(int cpu)
    > wake_up_process(p);
    > }
    >
    > + /* if any cpu succeeds, watchdog is considered enabled for the system */
    > + watchdog_enabled = 1;
    > +
    > return 0;
    > }
    >
    > @@ -452,9 +462,6 @@ static void watchdog_disable(int cpu)
    > per_cpu(softlockup_watchdog, cpu) = NULL;
    > kthread_stop(p);
    > }
    > -
    > - /* if any cpu succeeds, watchdog is considered enabled for the system */
    > - watchdog_enabled = 1;
    > }
    >
    > static void watchdog_enable_all_cpus(void)
    > --
    > 1.7.2.1


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