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    Subject[PATCH v7 23/24] watchdog: Introduce hardlockup_detector_mark_unavailable()
    Date
    The NMI watchdog may become unreliable during runtime. This is the case
    in x86 if, for instance, the HPET-based hardlockup detector is in use and
    the TSC counter becomes unstable.

    Introduce a new interface to mark the hardlockup detector as unavailable
    in such cases. When doing this, update the state of /proc/sys/kernel/
    nmi_watchdog to keep it consistent.

    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: "Ravi V. Shankar" <ravi.v.shankar@intel.com>
    Cc: iommu@lists.linux-foundation.org
    Cc: linuxppc-dev@lists.ozlabs.org
    Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    ---
    Changes since v6:
    * Introduced this patch

    Changes since v5:
    * N/A

    Changes since v4
    * N/A

    Changes since v3
    * N/A

    Changes since v2:
    * N/A

    Changes since v1:
    * N/A
    ---
    include/linux/nmi.h | 2 ++
    kernel/watchdog.c | 20 ++++++++++++++++++++
    2 files changed, 22 insertions(+)

    diff --git a/include/linux/nmi.h b/include/linux/nmi.h
    index a38c4509f9eb..40a97139ec65 100644
    --- a/include/linux/nmi.h
    +++ b/include/linux/nmi.h
    @@ -83,9 +83,11 @@ static inline void reset_hung_task_detector(void) { }

    #if defined(CONFIG_HARDLOCKUP_DETECTOR)
    extern void hardlockup_detector_disable(void);
    +extern void hardlockup_detector_mark_unavailable(void);
    extern unsigned int hardlockup_panic;
    #else
    static inline void hardlockup_detector_disable(void) {}
    +static inline void hardlockup_detector_mark_unavailable(void) {}
    #endif

    #if defined(CONFIG_HAVE_NMI_WATCHDOG) || defined(CONFIG_HARDLOCKUP_DETECTOR)
    diff --git a/kernel/watchdog.c b/kernel/watchdog.c
    index 8e61f21e7e33..0e4fed6d95b9 100644
    --- a/kernel/watchdog.c
    +++ b/kernel/watchdog.c
    @@ -47,6 +47,8 @@ static int __read_mostly nmi_watchdog_available;
    struct cpumask watchdog_cpumask __read_mostly;
    unsigned long *watchdog_cpumask_bits = cpumask_bits(&watchdog_cpumask);

    +static void __lockup_detector_reconfigure(void);
    +
    #ifdef CONFIG_HARDLOCKUP_DETECTOR

    # ifdef CONFIG_SMP
    @@ -85,6 +87,24 @@ static int __init hardlockup_panic_setup(char *str)
    }
    __setup("nmi_watchdog=", hardlockup_panic_setup);

    +/**
    + * hardlockup_detector_mark_unavailable - Mark the NMI watchdog as unavailable
    + *
    + * Indicate that the hardlockup detector has become unavailable. This may
    + * happen if the hardware resources that the detector uses have become
    + * unreliable.
    + */
    +void hardlockup_detector_mark_unavailable(void)
    +{
    + mutex_lock(&watchdog_mutex);
    +
    + /* These variables can be updated without stopping the detector. */
    + nmi_watchdog_user_enabled = 0;
    + nmi_watchdog_available = false;
    +
    + __lockup_detector_reconfigure();
    + mutex_unlock(&watchdog_mutex);
    +}
    #endif /* CONFIG_HARDLOCKUP_DETECTOR */

    /*
    --
    2.25.1
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