linux-kernel - Re: [PATCH AUTOSEL 5.15 14/28] watchdog: export lockup_detector

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Date:   Tue, 23 Aug 2022 11:34:15 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Michael Ellerman <mpe@...erman.id.au>, pmladek@...e.com,
        akpm@...ux-foundation.org, juri.lelli@...hat.com, pauld@...hat.com,
        nixiaoming@...wei.com, john.ogness@...utronix.de,
        frederic@...nel.org, linux@...musvillemoes.dk
Subject: Re: [PATCH AUTOSEL 5.15 14/28] watchdog: export
 lockup_detector_reconfigure

Le 14/08/2022 à 18:25, Sasha Levin a écrit :
> From: Laurent Dufour <ldufour@...ux.ibm.com>
> 
> [ Upstream commit 7c56a8733d0a2a4be2438a7512566e5ce552fccf ]

Hi Sasha,

Thanks for picking this patch.

Do you plan to pick the 2 others patches of this series in the older
kernels, as you did for 5.18 and 5.19 ?

The 2 other patches in this series are:
118b1366930c ("powerpc/pseries/mobility: set NMI watchdog factor during an
LPM")
f5e74e836097 ("powerpc/watchdog: introduce a NMI watchdog's factor")

I'm not sure how well they apply to these older kernels.

Thanks,
Laurent.

> 
> In some circumstances 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 with a factor, would prevent it to happen too frequently
> during LPM.
> 
> Rename lockup_detector_reconfigure() as __lockup_detector_reconfigure() and
> create a new function lockup_detector_reconfigure() calling
> __lockup_detector_reconfigure() under the protection of watchdog_mutex.
> 
> Signed-off-by: Laurent Dufour <ldufour@...ux.ibm.com>
> [mpe: Squash in build fix from Laurent, reported by Sachin]
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> Link: https://lore.kernel.org/r/20220713154729.80789-3-ldufour@linux.ibm.com
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  include/linux/nmi.h |  2 ++
>  kernel/watchdog.c   | 21 ++++++++++++++++-----
>  2 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/nmi.h b/include/linux/nmi.h
> index 750c7f395ca9..f700ff2df074 100644
> --- a/include/linux/nmi.h
> +++ b/include/linux/nmi.h
> @@ -122,6 +122,8 @@ int watchdog_nmi_probe(void);
>  int watchdog_nmi_enable(unsigned int cpu);
>  void watchdog_nmi_disable(unsigned int cpu);
>  
> +void lockup_detector_reconfigure(void);
> +
>  /**
>   * touch_nmi_watchdog - restart NMI watchdog timeout.
>   *
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index ad912511a0c0..1cfa269bd448 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -537,7 +537,7 @@ int lockup_detector_offline_cpu(unsigned int cpu)
>  	return 0;
>  }
>  
> -static void lockup_detector_reconfigure(void)
> +static void __lockup_detector_reconfigure(void)
>  {
>  	cpus_read_lock();
>  	watchdog_nmi_stop();
> @@ -557,6 +557,13 @@ static void lockup_detector_reconfigure(void)
>  	__lockup_detector_cleanup();
>  }
>  
> +void lockup_detector_reconfigure(void)
> +{
> +	mutex_lock(&watchdog_mutex);
> +	__lockup_detector_reconfigure();
> +	mutex_unlock(&watchdog_mutex);
> +}
> +
>  /*
>   * Create the watchdog infrastructure and configure the detector(s).
>   */
> @@ -573,13 +580,13 @@ static __init void lockup_detector_setup(void)
>  		return;
>  
>  	mutex_lock(&watchdog_mutex);
> -	lockup_detector_reconfigure();
> +	__lockup_detector_reconfigure();
>  	softlockup_initialized = true;
>  	mutex_unlock(&watchdog_mutex);
>  }
>  
>  #else /* CONFIG_SOFTLOCKUP_DETECTOR */
> -static void lockup_detector_reconfigure(void)
> +static void __lockup_detector_reconfigure(void)
>  {
>  	cpus_read_lock();
>  	watchdog_nmi_stop();
> @@ -587,9 +594,13 @@ static void lockup_detector_reconfigure(void)
>  	watchdog_nmi_start();
>  	cpus_read_unlock();
>  }
> +void lockup_detector_reconfigure(void)
> +{
> +	__lockup_detector_reconfigure();
> +}
>  static inline void lockup_detector_setup(void)
>  {
> -	lockup_detector_reconfigure();
> +	__lockup_detector_reconfigure();
>  }
>  #endif /* !CONFIG_SOFTLOCKUP_DETECTOR */
>  
> @@ -629,7 +640,7 @@ static void proc_watchdog_update(void)
>  {
>  	/* Remove impossible cpus to keep sysctl output clean. */
>  	cpumask_and(&watchdog_cpumask, &watchdog_cpumask, cpu_possible_mask);
> -	lockup_detector_reconfigure();
> +	__lockup_detector_reconfigure();
>  }
>  
>  /*