Re: [PATCH] rcu: Add BOOTPARAM_RCU_STALL_PANIC Kconfig option

["Paul E. McKenney" <paulmck@kernel.org>]

On Fri, Mar 13, 2026 at 09:56:49AM -0700, Gustavo Luiz Duarte wrote:
> Add a Kconfig option to set the default value of the
> kernel.panic_on_rcu_stall sysctl, allowing the kernel to be built
> with panic-on-RCU-stall enabled by default.
> 
> This is useful for high-availability systems that require automatic
> recovery (via panic_timeout) when a CPU stall is detected, without
> needing userspace to configure the sysctl at boot.
> 
> This follows the pattern established by BOOTPARAM_SOFTLOCKUP_PANIC
> and BOOTPARAM_HUNG_TASK_PANIC.  The runtime sysctl can still override
> the Kconfig default.
> 
> Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  kernel/rcu/Kconfig.debug | 24 ++++++++++++++++++++++++
>  kernel/rcu/tree_stall.h  |  2 +-
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
> index 625d75392647..fc2c775eeefc 100644
> --- a/kernel/rcu/Kconfig.debug
> +++ b/kernel/rcu/Kconfig.debug
> @@ -175,6 +175,30 @@ config RCU_CPU_STALL_NOTIFIER
>  	  Say Y here if you want RCU CPU stall notifiers (you don't want them)
>  	  Say N if you are unsure.
>  
> +config BOOTPARAM_RCU_STALL_PANIC
> +	bool "Panic (reboot) on RCU CPU stall"
> +	depends on RCU_STALL_COMMON
> +	default n
> +	help
> +	  Say Y here to enable the kernel to panic when an RCU CPU stall
> +	  is detected.
> +
> +	  The panic can be used in combination with panic_timeout,
> +	  to cause the system to reboot automatically after an
> +	  RCU CPU stall has been detected. This feature is useful for
> +	  high-availability systems that have uptime guarantees and
> +	  where a CPU stall must be resolved ASAP.
> +
> +	  The kernel.max_rcu_stall_to_panic sysctl can be used to set
> +	  a minimum number of stalls before panicking, allowing the
> +	  system to tolerate a given number of RCU CPU stalls before
> +	  triggering a panic.
> +
> +	  This setting can be overridden at runtime via the
> +	  kernel.panic_on_rcu_stall sysctl parameter.
> +
> +	  Say N if unsure.
> +
>  config RCU_TRACE
>  	bool "Enable tracing for RCU"
>  	depends on DEBUG_KERNEL
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index b67532cb8770..43ddabf46b5e 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -17,7 +17,7 @@
>  // Controlling CPU stall warnings, including delay calculation.
>  
>  /* panic() on RCU Stall sysctl. */
> -static int sysctl_panic_on_rcu_stall __read_mostly;
> +static int sysctl_panic_on_rcu_stall __read_mostly = IS_ENABLED(CONFIG_BOOTPARAM_RCU_STALL_PANIC);
>  static int sysctl_max_rcu_stall_to_panic __read_mostly;
>  
>  static const struct ctl_table rcu_stall_sysctl_table[] = {
> 
> ---
> base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681
> change-id: 20260313-panic_on_rcustall-95709d1abf2f
> 
> Best regards,
> -- 
> Gustavo Luiz Duarte <gustavold@gmail.com>
>