Subject: Re: [PATCH v2 2/4] watchdog: export watchdog_mutex and lockup_detector_reconfigure

From: Michael Ellerman <[email-masked]>
Date: Fri, 24 Jun 2022 16:31:55 +1000

Laurent Dufour <[email-masked]> writes:
> In some cricunstances it may be interesting to reconfigure the watchdog
> from inside the kernel.
>
> On PowerPC, this may helpful before and after a LPAR migration (LPM) is
> initiated, because it implies some latencies, watchdog, and especially NMI
> watchdog is expected to be triggered during this operation. Reconfiguring
> the watchdog, would prevent it to happen too frequently during LPM.
>
> The watchdog_mutex is exported to allow some variable to be changed under
> its protection and prevent any conflict.
> The lockup_detector_reconfigure() function is exported and is expected to
> be called under the protection of watchdog_mutex.
>
> Signed-off-by: Laurent Dufour <[email-masked]>
> ---
>  include/linux/nmi.h | 3 +++
>  kernel/watchdog.c   | 6 +++---
>  2 files changed, 6 insertions(+), 3 deletions(-)

Is there a maintainer for kernel/watchdog.c ?

There's Wim & Guenter at linux-watchdog@vger but I think that's only for
drivers/watchdog?

Maybe we should Cc that list anyway?

> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
> index 750c7f395ca9..84300fb0f90a 100644
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -122,6 +122,9 @@ int watchdog_nmi_probe(void);
>  int watchdog_nmi_enable(unsigned int cpu);
>  void watchdog_nmi_disable(unsigned int cpu);
>  
> +extern struct mutex watchdog_mutex;
> +void lockup_detector_reconfigure(void);

It would be preferable if we didn't export the mutex.

I think you could arrange that by ...

Renaming lockup_detector_configure() to __lockup_detector_configure()
and then adding a new lockup_detector_configure() that is non-static and
takes the lock around __lockup_detector_configure().

cheers