Re: [PATCH] panic: only warn about deprecated panic_print on write access

[Feng Tang]

Hi Gal,

Thanks for the fix!

On Tue, Jan 06, 2026 at 06:33:21PM +0200, Gal Pressman wrote:
> The panic_print_deprecated() warning is being triggered on both read and
> write operations to the panic_print parameter.
> 
> This causes spurious warnings when users run 'sysctl -a' to list all
> sysctl values, since that command reads /proc/sys/kernel/panic_print and
> triggers the deprecation notice.
> 
> Modify the handlers to only emit the deprecation warning when the
> parameter is actually being set:
> 
>  - sysctl_panic_print_handler(): check 'write' flag before warning.
>  - panic_print_get(): remove the deprecation call entirely.
> 
> This way, users are only warned when they actively try to use the
> deprecated parameter, not when passively querying system state.
> 
> Fixes: ee13240cd78b ("panic: add note that panic_print sysctl interface is deprecated")
> Fixes: 2683df6539cb ("panic: add note that 'panic_print' parameter is deprecated")
> Cc: Feng Tang <feng.tang@xxxxxxxxxxxxxxxxx>
> Reviewed-by: Mark Bloch <mbloch@xxxxxxxxxx>
> Reviewed-by: Nimrod Oren <noren@xxxxxxxxxx>
> Signed-off-by: Gal Pressman <gal@xxxxxxxxxx>
> ---
>  kernel/panic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 0d52210a9e2b..0c20fcaae98a 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -131,7 +131,8 @@ static int proc_taint(const struct ctl_table *table, int write,
>  static int sysctl_panic_print_handler(const struct ctl_table *table, int write,
>  			   void *buffer, size_t *lenp, loff_t *ppos)
>  {
> -	panic_print_deprecated();
> +	if (write)
> +		panic_print_deprecated();

This makes sense to me, as 'sysctl -a' is a very common usage.

>  	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
>  }
>  
> @@ -1014,7 +1015,6 @@ static int panic_print_set(const char *val, const struct kernel_param *kp)
>  
>  static int panic_print_get(char *val, const struct kernel_param *kp)
>  {
> -	panic_print_deprecated();

Actually this was intentional, in one of the patch version, this
panic_print_get() was not there but reusing the param_get_ulong().

It was added later as sometimes developer do want to runtime check
the current 'panic_print' setting through /sys/module/kernel/parameters/
interface, and I thought it may be better to give the warning.

Thanks,
Feng

>  	return  param_get_ulong(val, kp);
>  }
>  
> -- 
> 2.40.1