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

[Petr Mladek <pmladek@suse.com>]

On Mon 2026-01-12 08:48:37, Gal Pressman wrote:
> On 12/01/2026 5:32, Feng Tang wrote:
> > On Sun, Jan 11, 2026 at 10:28:55AM +0200, Gal Pressman wrote:
> >> On 08/01/2026 17:52, Petr Mladek wrote:
> >>> On Wed 2026-01-07 15:20:44, Feng Tang wrote:
> >>>> On Wed, Jan 07, 2026 at 08:41:22AM +0200, Gal Pressman wrote:
> >>>>> On 07/01/2026 5:00, Feng Tang wrote:
> >>>>>>> @@ -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.
> >>>>>
> >>>>> I figured it would make sense to keep the behaviors consistent.
> >>>
> >>> I see.
> >>>
> >>>> When people run 'sysctl -a', in 99.9% cases, the users don't care
> >>>> 'panic_print' or even don't know what 'panic_print' is, that's why
> >>>> I think removing it makes sense.
> >>>>
> >>>> But for a user running 'cat /sys/module/kernel/parameters/panic_rint',
> >>>> giving a warning is meaningful.
> >>>
> >>> Makes perfect sense.
> >>>
> >>> We need to make people aware that "panic_print" will eventually go
> >>> away. 'sysctl -a' is different because it prints all values and
> >>> there is big chance that the caller is not interested in "panic_print"
> >>> at all.
> >>>
> >>> It makes sense to remove the warning from sysctl read. But I would
> >>> keep it in sysfs read.
> >>
> >> The sysfs entry exhibits the same issue, just different command:
> >>
> >> # systool -m kernel -v
> >>
> >> Or:
> >>
> >> # grep . /sys/module/kernel/parameters/*

I see.

> > Yes, when user checks the kernel parameters, I think it's better to
> > give them a notice (it's a pr_info_once(), which only prints once
> > for the whole power cycle).
> This log message causes a lot of noise for people who have no idea what
> panic_print is.
> We started seeing this print internally, and it took a long time and
> significant resources to figure out what changed and if we were doing
> anything wrong in our environments.
> 
> Seeing a deprecation notice is alarming, especially if you don't know
> what is being deprecated or how it affects you. In my opinion, we
> shouldn't print this unless someone actually uses panic_print.

I am fine with printing the warning only when the value is
modified (set/write).

Best Regards,
Petr

PS: Sigh, it is hard to change or remove an interface. It is always
    better to think twice before introducing one.