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    SubjectRe: fix BUG: using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog
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    On Fri, 2010-08-13 at 13:21 +0300, Sergey Senozhatsky wrote:

    > [ 67.703556] BUG: using smp_processor_id() in preemptible [00000000] code: s2disk/5139
    > [ 67.703563] caller is touch_nmi_watchdog+0x15/0x2c
    > [ 67.703566] Pid: 5139, comm: s2disk Not tainted 2.6.36-rc0-git12-07921-g60bf26a-dirty #116
    > [ 67.703568] Call Trace:
    > [ 67.703575] [<ffffffff811f6bf1>] debug_smp_processor_id+0xc9/0xe4
    > [ 67.703578] [<ffffffff81092766>] touch_nmi_watchdog+0x15/0x2c
    > [ 67.703584] [<ffffffff81222950>] acpi_os_stall+0x34/0x40
    > [ 67.703589] [<ffffffff812398d2>] acpi_ex_system_do_stall+0x34/0x38

    Which could mean two things, either ACPI got funny on us, or Don's new
    watchdog stuff has a hole in it.


    > ---
    >
    > diff --git a/kernel/watchdog.c b/kernel/watchdog.c
    > index 613bc1f..8822f1e 100644
    > --- a/kernel/watchdog.c
    > +++ b/kernel/watchdog.c
    > @@ -116,13 +116,14 @@ static unsigned long get_sample_period(void)
    > static void __touch_watchdog(void)
    > {
    > int this_cpu = smp_processor_id();
    > -
    > - __get_cpu_var(watchdog_touch_ts) = get_timestamp(this_cpu);
    > + per_cpu(watchdog_touch_ts, this_cpu) = get_timestamp(this_cpu);
    > }

    That change seems sensible enough..

    > void touch_softlockup_watchdog(void)
    > {
    > - __get_cpu_var(watchdog_touch_ts) = 0;
    > + int this_cpu = get_cpu();
    > + per_cpu(watchdog_touch_ts, this_cpu) = 0;
    > + put_cpu();
    > }
    > EXPORT_SYMBOL(touch_softlockup_watchdog);
    >
    > @@ -142,7 +143,9 @@ void touch_all_softlockup_watchdogs(void)
    > #ifdef CONFIG_HARDLOCKUP_DETECTOR
    > void touch_nmi_watchdog(void)
    > {
    > - __get_cpu_var(watchdog_nmi_touch) = true;
    > + int this_cpu = get_cpu();
    > + per_cpu(watchdog_nmi_touch, this_cpu) = true;
    > + put_cpu();
    > touch_softlockup_watchdog();
    > }
    > EXPORT_SYMBOL(touch_nmi_watchdog);

    These other two really are about assumptions we make on the call sites,
    which at the very least are violated by ACPI.

    Don/Ingo, remember if we require touch_*_watchdog callers to have
    preemption disabled? Or is the proposed patch sensible?



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