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    Subject[tip:core/urgent] watchdog/hardlockup: Provide interface to stop/restart perf events
    Commit-ID:  d0b6e0a8ef24b1b07078ababe5d91bcdf4f4264a
    Gitweb: http://git.kernel.org/tip/d0b6e0a8ef24b1b07078ababe5d91bcdf4f4264a
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Tue, 12 Sep 2017 21:36:55 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Thu, 14 Sep 2017 11:41:03 +0200

    watchdog/hardlockup: Provide interface to stop/restart perf events

    Provide an interface to stop and restart perf NMI watchdog events on all
    CPUs. This is only usable during init and especially for handling the perf
    HT bug on Intel machines. It's safe to use it this way as nothing can
    start/stop the NMI watchdog in parallel.

    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Don Zickus <dzickus@redhat.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Chris Metcalf <cmetcalf@mellanox.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Nicholas Piggin <npiggin@gmail.com>
    Cc: Sebastian Siewior <bigeasy@linutronix.de>
    Cc: Ulrich Obergfell <uobergfe@redhat.com>
    Link: http://lkml.kernel.org/r/20170912194146.167649596@linutronix.de
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    include/linux/nmi.h | 4 ++++
    kernel/watchdog_hld.c | 41 +++++++++++++++++++++++++++++++++++++++++
    2 files changed, 45 insertions(+)

    diff --git a/include/linux/nmi.h b/include/linux/nmi.h
    index a36abe2..b24d4a5 100644
    --- a/include/linux/nmi.h
    +++ b/include/linux/nmi.h
    @@ -75,7 +75,11 @@ static inline void hardlockup_detector_disable(void) {}

    #if defined(CONFIG_HARDLOCKUP_DETECTOR_PERF)
    extern void arch_touch_nmi_watchdog(void);
    +extern void hardlockup_detector_perf_stop(void);
    +extern void hardlockup_detector_perf_restart(void);
    #else
    +static inline void hardlockup_detector_perf_stop(void) { }
    +static inline void hardlockup_detector_perf_restart(void) { }
    #if !defined(CONFIG_HAVE_NMI_WATCHDOG)
    static inline void arch_touch_nmi_watchdog(void) {}
    #endif
    diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
    index 3a09ea1..c9586eb 100644
    --- a/kernel/watchdog_hld.c
    +++ b/kernel/watchdog_hld.c
    @@ -261,3 +261,44 @@ void watchdog_nmi_disable(unsigned int cpu)
    firstcpu_err = 0;
    }
    }
    +
    +/**
    + * hardlockup_detector_perf_stop - Globally stop watchdog events
    + *
    + * Special interface for x86 to handle the perf HT bug.
    + */
    +void __init hardlockup_detector_perf_stop(void)
    +{
    + int cpu;
    +
    + lockdep_assert_cpus_held();
    +
    + for_each_online_cpu(cpu) {
    + struct perf_event *event = per_cpu(watchdog_ev, cpu);
    +
    + if (event)
    + perf_event_disable(event);
    + }
    +}
    +
    +/**
    + * hardlockup_detector_perf_restart - Globally restart watchdog events
    + *
    + * Special interface for x86 to handle the perf HT bug.
    + */
    +void __init hardlockup_detector_perf_restart(void)
    +{
    + int cpu;
    +
    + lockdep_assert_cpus_held();
    +
    + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
    + return;
    +
    + for_each_online_cpu(cpu) {
    + struct perf_event *event = per_cpu(watchdog_ev, cpu);
    +
    + if (event)
    + perf_event_enable(event);
    + }
    +}
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