Re: [PATCH] Documentation: Better document the softlockup_panic sysctl

[Kees Cook <keescook@chromium.org>]

On Tue, Mar 10, 2020 at 12:15:03PM -0300, Guilherme G. Piccoli wrote:
> Commit 9c44bc03fff4 ("softlockup: allow panic on lockup") added the
> softlockup_panic sysctl, but didn't add information about it to the file
> Documentation/admin-guide/sysctl/kernel.rst (which in that time certainly
> wasn't rst and had other name!).
> 
> This patch just adds the respective documentation and references it from
> the corresponding entry in Documentation/admin-guide/kernel-parameters.txt.
> 
> This patch was strongly based on Scott Wood's commit d22881dc13b6
> ("Documentation: Better document the hardlockup_panic sysctl").
> 
> Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  6 +++---
>  Documentation/admin-guide/sysctl/kernel.rst     | 13 +++++++++++++
>  2 files changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index c07815d230bc..adf77ead02c3 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4515,9 +4515,9 @@
>  
>  			A nonzero value instructs the soft-lockup detector
>  			to panic the machine when a soft-lockup occurs. This
> -			is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
> -			which is the respective build-time switch to that
> -			functionality.
> +			is also controlled by kernel.softlockup_panic sysctl
> +			and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the
> +			respective build-time switch to that functionality.
>  
>  	softlockup_all_cpu_backtrace=
>  			[KNL] Should the soft-lockup detector generate
> diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> index def074807cee..95b2f3256323 100644
> --- a/Documentation/admin-guide/sysctl/kernel.rst
> +++ b/Documentation/admin-guide/sysctl/kernel.rst
> @@ -95,6 +95,7 @@ show up in /proc/sys/kernel:
>  - shmmax                      [ sysv ipc ]
>  - shmmni
>  - softlockup_all_cpu_backtrace
> +- softlockup_panic
>  - soft_watchdog
>  - stack_erasing
>  - stop-a                      [ SPARC only ]
> @@ -1029,6 +1030,18 @@ NMI.
>  1: on detection capture more debug information.
>  
>  
> +softlockup_panic:
> +=================
> +
> +This parameter can be used to control whether the kernel panics when
> +a soft lockup is detected.
> +
> +0: don't panic on soft lockup
> +1: panic on soft lockup
> +
> +This can also be set using the softlockup_panic kernel parameter.
> +
> +
>  soft_watchdog:
>  ==============
>  
> -- 
> 2.24.1
> 

-- 
Kees Cook