tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

panic: introduce helper functions for panic state

Patch series "panic: introduce panic status function family", v2.

This series introduces a family of helper functions to manage panic state
and updates existing code to use them.

Before this series, panic state helpers were scattered and inconsistent.
For example, panic_in_progress() was defined in printk/printk.c, not in
panic.c or panic.h. As a result, developers had to look in unexpected
places to understand or re-use panic state logic. Other checks were open-
coded, duplicating logic across panic, crash, and watchdog paths.

The new helpers centralize the functionality in panic.c/panic.h:
- panic_try_start()
- panic_reset()
- panic_in_progress()
- panic_on_this_cpu()
- panic_on_other_cpu()

Patches 1–8 add the helpers and convert panic/crash and printk/nbcon
code to use them.

Patch 9 fixes a bug in the watchdog subsystem by skipping checks when a
panic is in progress, avoiding interference with the panic CPU.

Together, this makes panic state handling simpler, more discoverable, and
more robust.


This patch (of 9):

This patch introduces four new helper functions to abstract the management
of the panic_cpu variable. These functions will be used in subsequent
patches to refactor existing code.

The direct use of panic_cpu can be error-prone and ambiguous, as it
requires manual checks to determine which CPU is handling the panic. The
new helpers clarify intent:

panic_try_start():
Atomically sets the current CPU as the panicking CPU.

panic_reset():
Reset panic_cpu to PANIC_CPU_INVALID.

panic_in_progress():
Checks if a panic has been triggered.

panic_on_this_cpu():
Returns true if the current CPU is the panic originator.

panic_on_other_cpu():
Returns true if a panic is on another CPU.

This change lays the groundwork for improved code readability
and robustness in the panic handling subsystem.

Link: https://lkml.kernel.org/r/20250825022947.1596226-1-wangjinchao600@gmail.com
Link: https://lkml.kernel.org/r/20250825022947.1596226-2-wangjinchao600@gmail.com
Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
Cc: Anna Schumaker <anna.schumaker@oracle.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Doug Anderson <dianders@chromium.org>
Cc: "Guilherme G. Piccoli" <gpiccoli@igalia.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Kees Cook <kees@kernel.org>
Cc: Li Huafei <lihuafei1@huawei.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: Luo Gengkun <luogengkun@huaweicloud.com>
Cc: Max Kellermann <max.kellermann@ionos.com>
Cc: Nam Cao <namcao@linutronix.de>
Cc: oushixiong <oushixiong@kylinos.cn>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Qianqiang Liu <qianqiang.liu@163.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Sohil Mehta <sohil.mehta@intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleinxer <tglx@linutronix.de>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Thorsten Blum <thorsten.blum@linux.dev>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Yicong Yang <yangyicong@hisilicon.com>
Cc: Yunhui Cui <cuiyunhui@bytedance.com>
Cc: Yury Norov (NVIDIA) <yury.norov@gmail.com>b
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

authored by

Jinchao Wang and committed by
Andrew Morton d0d9c723 e40d2014

+59 -5
+6
include/linux/panic.h
··· 43 43 extern atomic_t panic_cpu; 44 44 #define PANIC_CPU_INVALID -1 45 45 46 + bool panic_try_start(void); 47 + void panic_reset(void); 48 + bool panic_in_progress(void); 49 + bool panic_on_this_cpu(void); 50 + bool panic_on_other_cpu(void); 51 + 46 52 /* 47 53 * Only to be used by arch init code. If the user over-wrote the default 48 54 * CONFIG_PANIC_TIMEOUT, honor it.
+53
kernel/panic.c
··· 299 299 300 300 atomic_t panic_cpu = ATOMIC_INIT(PANIC_CPU_INVALID); 301 301 302 + bool panic_try_start(void) 303 + { 304 + int old_cpu, this_cpu; 305 + 306 + /* 307 + * Only one CPU is allowed to execute the crash_kexec() code as with 308 + * panic(). Otherwise parallel calls of panic() and crash_kexec() 309 + * may stop each other. To exclude them, we use panic_cpu here too. 310 + */ 311 + old_cpu = PANIC_CPU_INVALID; 312 + this_cpu = raw_smp_processor_id(); 313 + 314 + return atomic_try_cmpxchg(&panic_cpu, &old_cpu, this_cpu); 315 + } 316 + EXPORT_SYMBOL(panic_try_start); 317 + 318 + void panic_reset(void) 319 + { 320 + atomic_set(&panic_cpu, PANIC_CPU_INVALID); 321 + } 322 + EXPORT_SYMBOL(panic_reset); 323 + 324 + bool panic_in_progress(void) 325 + { 326 + return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID); 327 + } 328 + EXPORT_SYMBOL(panic_in_progress); 329 + 330 + /* Return true if a panic is in progress on the current CPU. */ 331 + bool panic_on_this_cpu(void) 332 + { 333 + /* 334 + * We can use raw_smp_processor_id() here because it is impossible for 335 + * the task to be migrated to the panic_cpu, or away from it. If 336 + * panic_cpu has already been set, and we're not currently executing on 337 + * that CPU, then we never will be. 338 + */ 339 + return unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id()); 340 + } 341 + EXPORT_SYMBOL(panic_on_this_cpu); 342 + 343 + /* 344 + * Return true if a panic is in progress on a remote CPU. 345 + * 346 + * On true, the local CPU should immediately release any printing resources 347 + * that may be needed by the panic CPU. 348 + */ 349 + bool panic_on_other_cpu(void) 350 + { 351 + return (panic_in_progress() && !this_cpu_in_panic()); 352 + } 353 + EXPORT_SYMBOL(panic_on_other_cpu); 354 + 302 355 /* 303 356 * A variant of panic() called from NMI context. We return if we've already 304 357 * panicked on this CPU. If another CPU already panicked, loop in
-5
kernel/printk/printk.c
··· 345 345 } 346 346 #define up_console_sem() __up_console_sem(_RET_IP_) 347 347 348 - static bool panic_in_progress(void) 349 - { 350 - return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID); 351 - } 352 - 353 348 /* Return true if a panic is in progress on the current CPU. */ 354 349 bool this_cpu_in_panic(void) 355 350 {