Re: [linux-next:master 9966/13055] kernel/watchdog.c:74:22: warning: unused variable 'hardlockup_si_mask'

Petr Mladek
2025-12-04T13:38:49Z

On Wed 2025-12-03 14:44:53, Andrew Morton wrote:
> On Wed, 3 Dec 2025 09:05:30 +0800 kernel test robot <lkp@intel.com> wrote:
>
> > tree: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> > head: 47b7b5e32bb7264b51b89186043e1ada4090b558
> > commit: a9af76a78760717361cccc884dc649e30db61c8b [9966/13055] watchdog: add sys_info sysctls to dump sys info on system lockup
> > config: powerpc64-randconfig-002-20251203 (https://download.01.org/0day-ci/archive/20251203/202512030920.NFKtekA7-lkp@intel.com/config)
> > compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 734a912d0f025559fcf76bde9aaaeb0383c1625a)
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251203/202512030920.NFKtekA7-lkp@intel.com/reproduce)
> >
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202512030920.NFKtekA7-lkp@intel.com/
> >
> > All warnings (new ones prefixed by >>):
> >
> > >> kernel/watchdog.c:74:22: warning: unused variable 'hardlockup_si_mask' [-Wunused-variable]
> > 74 | static unsigned long hardlockup_si_mask;
> > | ^~~~~~~~~~~~~~~~~~
> > 1 warning generated.
>
> I'm testing the appended patch but it needs checking please.
>
> The comment for hardlockup_si_mask says
>
> * bitmask to control what kinds of system info to be printed when
> * hard lockup is detected, it could be task, memory, lock etc.
> * Refer include/linux/sys_info.h for detailed bit definition.
>
> but the variable depends on "COUNTS_HRTIMER". The comment doesn't
> mention hrtimers and I don't see why it should. Not sure what's going
> on here.

Good point! It took me some time to understand it.

So, powerpc implements its own watchog, see arch/powerpc/kernel/watchdog.c.
The watchdog is supported only by some powerpc platforms, see the
following line in arch/powerpc/Kconfig:

select HAVE_HARDLOCKUP_DETECTOR_ARCH if PPC_BOOK3S_64 && SMP

As a result, the test system could have the following in the config,
see https://download.01.org/0day-ci/archive/20251203/202512030920.NFKtekA7-lkp@intel.com/config

CONFIG_HARDLOCKUP_DETECTOR=y
# CONFIG_HARDLOCKUP_DETECTOR_PERF is not set
# CONFIG_HARDLOCKUP_DETECTOR_BUDDY is not set
CONFIG_HARDLOCKUP_DETECTOR_ARCH=y

And "COUNTS_HRTIMER" is not defined.

> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: kernel/watchdog.c: fix unused var warning
> Date: Wed Dec 3 02:34:40 PM PST 2025
>
> >> kernel/watchdog.c:74:22: warning: unused variable 'hardlockup_si_mask' [-Wunused-variable]
> 74 | static unsigned long hardlockup_si_mask;
> | ^~~~~~~~~~~~~~~~~~
> 1 warning generated.
>
> Fixes: a9af76a78760 ("watchdog: add sys_info sysctls to dump sys info on system lockup")
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202512030920.NFKtekA7-lkp@intel.com/
> Link: https://lkml.kernel.org/r/202512030920.NFKtekA7-lkp@intel.com
> Cc: Feng Tang <feng.tang@linux.alibaba.com>
> Cc: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> kernel/watchdog.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> --- a/kernel/watchdog.c~kernel-watchdogc-fix-unused-var-warning
> +++ a/kernel/watchdog.c
> @@ -66,13 +66,6 @@ int __read_mostly sysctl_hardlockup_all_
> unsigned int __read_mostly hardlockup_panic =
> IS_ENABLED(CONFIG_BOOTPARAM_HARDLOCKUP_PANIC);
>
> -/*
> - * bitmasks to control what kinds of system info to be printed when
> - * hard lockup is detected, it could be task, memory, lock etc.
> - * Refer include/linux/sys_info.h for detailed bit definition.
> - */
> -static unsigned long hardlockup_si_mask;
> -
> #ifdef CONFIG_SYSFS
>
> static unsigned int hardlockup_count;
> @@ -135,6 +128,13 @@ __setup("nmi_watchdog=", hardlockup_pani
>
> #if defined(CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER)
>
> +/*
> + * bitmask to control what kinds of system info to be printed when
> + * hard lockup is detected, it could be task, memory, lock etc.
> + * Refer include/linux/sys_info.h for detailed bit definition.
> + */
> +static unsigned long hardlockup_si_mask;
> +
> static DEFINE_PER_CPU(atomic_t, hrtimer_interrupts);
> static DEFINE_PER_CPU(int, hrtimer_interrupts_saved);
> static DEFINE_PER_CPU(bool, watchdog_hardlockup_warned);
> @@ -1250,6 +1250,7 @@ static const struct ctl_table watchdog_s
> .extra1 = SYSCTL_ZERO,
> .extra2 = SYSCTL_ONE,
> },
> +#if defined(CONFIG_HARDLOCKUP_DETECTOR_COUNTS_HRTIMER)
> {
> .procname = "hardlockup_sys_info",
> .data = &hardlockup_si_mask,
> @@ -1257,6 +1258,7 @@ static const struct ctl_table watchdog_s
> .mode = 0644,
> .proc_handler = sysctl_sys_info_handler,
> },
> +#endif
> #ifdef CONFIG_SMP
> {
> .procname = "hardlockup_all_cpu_backtrace",
> _

This patch makes some sense because the arch-specific watchdog does
not support the sys_info interface. And it is better than nothing.
definitely.

A better solution would be export the variable and handle it
in arch/powerpc/kernel/watchdog.c.

It seems that powerpc is the only architecture which could define
HAVE_HARDLOCKUP_DETECTOR_ARCH.

Feng, would you have time to look at it?

Best Regards,
Petr