Re: [patch V2 25/29] lockup_detector: Implement init time detection of perf

Don Zickus
2017-09-13T18:02:44Z

On Tue, Sep 12, 2017 at 09:37:19PM +0200, Thomas Gleixner wrote:
> Use the init time detection of the perf NMI watchdog to determine whether
> the perf NMI watchdog is functional. If not disable it permanentely. It
> won't come back magically at runtime.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Don Zickus <dzickus@redhat.com>
> Cc: Chris Metcalf <cmetcalf@mellanox.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Sebastian Siewior <bigeasy@linutronix.de>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Ulrich Obergfell <uobergfe@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Link: http://lkml.kernel.org/r/20170831073054.997264122@linutronix.de
>
> ---
> kernel/watchdog.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -44,6 +44,7 @@ int __read_mostly watchdog_user_enabled
> int __read_mostly nmi_watchdog_user_enabled = NMI_WATCHDOG_DEFAULT;
> int __read_mostly soft_watchdog_user_enabled = 1;
> int __read_mostly watchdog_thresh = 10;
> +int __read_mostly nmi_watchdog_available;
>
> struct cpumask watchdog_allowed_mask __read_mostly;
> static bool softlockup_threads_initialized __read_mostly;
> @@ -114,6 +115,12 @@ void __weak watchdog_nmi_disable(unsigne
> hardlockup_detector_perf_disable();
> }
>
> +/* Return 0, if a NMI watchdog is available. Error code otherwise */
> +int __weak __init void watchdog_nmi_probe(void)

^^^ compile error, can't have 'int' and 'void'. Removing 'void' fixes it.

Cheers,
Don

> +{
> + return hardlockup_detector_perf_init();
> +}
> +
> /**
> * watchdog_nmi_reconfigure - Optional function to reconfigure NMI watchdogs
> * @run: If false stop the watchdogs on all enabled CPUs
> @@ -145,7 +152,7 @@ static void lockup_detector_update_enabl
> watchdog_enabled = 0;
> if (!watchdog_user_enabled)
> return;
> - if (nmi_watchdog_user_enabled)
> + if (nmi_watchdog_available && nmi_watchdog_user_enabled)
> watchdog_enabled |= NMI_WATCHDOG_ENABLED;
> if (soft_watchdog_user_enabled)
> watchdog_enabled |= SOFT_WATCHDOG_ENABLED;
> @@ -692,6 +699,8 @@ int proc_watchdog(struct ctl_table *tabl
> int proc_nmi_watchdog(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp, loff_t *ppos)
> {
> + if (!nmi_watchdog_available && write)
> + return -ENOTSUPP;
> return proc_watchdog_common(NMI_WATCHDOG_ENABLED,
> table, write, buffer, lenp, ppos);
> }
> @@ -764,5 +773,7 @@ void __init lockup_detector_init(void)
> cpumask_copy(&watchdog_cpumask, cpu_possible_mask);
> #endif
>
> + if (!watchdog_nmi_probe())
> + nmi_watchdog_available = true;
> softlockup_init_threads();
> }
>
>