Re: [PATCH] panic/kexec: Allow forcing panic execution on a specific CPU

[kernel test robot <lkp@intel.com>]

Hi Pnina,

kernel test robot noticed the following build warnings:

[auto build test WARNING on akpm-mm/mm-everything]
[also build test WARNING on linus/master v6.19-rc3 next-20251219]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Pnina-Feder/panic-kexec-Allow-forcing-panic-execution-on-a-specific-CPU/20260101-203448
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20260101123237.277411-1-pnina.feder%40mobileye.com
patch subject: [PATCH] panic/kexec: Allow forcing panic execution on a specific CPU
config: arm64-randconfig-r122-20260104 (https://download.01.org/0day-ci/archive/20260104/202601041820.6M8cIq2e-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 9b8addffa70cee5b2acc5454712d9cf78ce45710)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260104/202601041820.6M8cIq2e-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/202601041820.6M8cIq2e-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/panic.c:349:69: warning: diagnostic behavior may be improved by adding the 'format(printf, 1, 0)' attribute to the declaration of 'panic_force_target_cpu' [-Wmissing-format-attribute]
     321 |         vsnprintf(panic_redirect_msg, sizeof(panic_redirect_msg), fmt, args);
         |                                                                            ^
   kernel/panic.c:321:13: note: 'panic_force_target_cpu' declared here
     321 | static bool panic_force_target_cpu(const char *fmt, va_list args)
         |             ^
   1 warning generated.


vim +349 kernel/panic.c

   308	
   309	/**
   310	 * panic_force_target_cpu - Redirect panic to a specific CPU for crash kernel
   311	 * @fmt: panic message format string
   312	 * @args: arguments for format string
   313	 *
   314	 * Some platforms require panic handling to occur on a specific CPU
   315	 * for the crash kernel to function correctly. This function redirects
   316	 * panic handling to CONFIG_PANIC_FORCE_CPU_ID before kexec.
   317	 *
   318	 * Returns true if panic should proceed on current CPU.
   319	 * Returns false (never returns) if panic was redirected.
   320	 */
   321	static bool panic_force_target_cpu(const char *fmt, va_list args)
   322	{
   323		static char panic_redirect_msg[1024];
   324		int cpu = raw_smp_processor_id();
   325		int target_cpu = CONFIG_PANIC_FORCE_CPU_ID;
   326	
   327		/* Already on target CPU - proceed normally */
   328		if (cpu == target_cpu)
   329			return true;
   330	
   331		/* Target CPU is offline, can't redirect */
   332		if (!cpu_online(target_cpu)) {
   333			pr_warn("panic: CPU %d is offline, cannot redirect panic. "
   334				"Crash kernel interrupts may be unavailable.\n", target_cpu);
   335			return true;
   336		}
   337	
   338		/* Another panic already in progress */
   339		if (panic_in_progress()) {
   340			pr_warn("panic: Another panic in progress on CPU %d, cannot redirect to CPU %d. "
   341				"Crash kernel interrupts may be unavailable.\n",
   342				atomic_read(&panic_cpu), target_cpu);
   343			return true;
   344		}
   345	
   346		pr_info("panic: Redirecting from CPU %d to CPU %d for crash kernel\n",
   347			cpu, target_cpu);
   348	
 > 349		vsnprintf(panic_redirect_msg, sizeof(panic_redirect_msg), fmt, args);
   350	
   351		smp_call_function_single(target_cpu, do_panic_on_target_cpu, panic_redirect_msg, false);
   352	
   353		return false;
   354	}
   355	#else
   356	static inline bool panic_force_target_cpu(const char *fmt, va_list args)
   357	{
   358		return true;
   359	}
   360	#endif /* CONFIG_PANIC_FORCE_CPU */
   361	

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