Selected crash callbacks should not require running every panic notifier before kdump. Add a separate atomic chain with an at-most-once dispatch helper, and invoke it before panic reaches the kmsg dumpers.
The helper permits another call from the crash path without repeating callbacks or recursing into them. Document that callbacks may run in NMI context, with other CPUs running and the kexec lock held. Link: https://lore.kernel.org/r/[email protected] Signed-off-by: Zack Rusin <[email protected]> --- New in v2: separate pre-kdump chain, with a set-once dispatch guard. include/linux/panic_notifier.h | 3 +++ kernel/panic.c | 26 ++++++++++++++++++++++++++ 2 files changed, 29 insertions(+) diff --git a/include/linux/panic_notifier.h b/include/linux/panic_notifier.h index 41e32483d7a7..3ad390764a41 100644 --- a/include/linux/panic_notifier.h +++ b/include/linux/panic_notifier.h @@ -6,6 +6,9 @@ #include <linux/types.h> extern struct atomic_notifier_head panic_notifier_list; +extern struct atomic_notifier_head panic_pre_kdump_list; + +void panic_notify_pre_kdump(char *msg); extern bool crash_kexec_post_notifiers; diff --git a/kernel/panic.c b/kernel/panic.c index 213725b612aa..d78e90abb192 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -82,6 +82,10 @@ ATOMIC_NOTIFIER_HEAD(panic_notifier_list); EXPORT_SYMBOL(panic_notifier_list); +struct atomic_notifier_head panic_pre_kdump_list = + ATOMIC_NOTIFIER_INIT(panic_pre_kdump_list); +EXPORT_SYMBOL_GPL(panic_pre_kdump_list); + static void panic_print_deprecated(void) { pr_info_once("Kernel: The 'panic_print' parameter is now deprecated. Please use 'panic_sys_info' and 'panic_console_replay' instead.\n"); @@ -567,6 +571,27 @@ static void panic_other_cpus_shutdown(bool crash_kexec) crash_smp_send_stop(); } +/** + * panic_notify_pre_kdump - invoke selected callbacks before kdump + * @msg: Panic message, or NULL for direct crash-kexec entry + * + * Dispatch at most once per boot, including recursive entry. Callbacks run + * with interrupts disabled, possibly in NMI context, before other CPUs have + * necessarily stopped. The kexec lock may be held. They must not sleep, + * allocate, wait for other CPUs, or call into kexec management operations. + * The message is read-only and may only be used during the callback. + */ +void panic_notify_pre_kdump(char *msg) +{ + static atomic_t started = ATOMIC_INIT(0); + unsigned long flags; + + local_irq_save(flags); + if (!atomic_xchg(&started, 1)) + atomic_notifier_call_chain(&panic_pre_kdump_list, 0, msg); + local_irq_restore(flags); +} + /** * vpanic - halt the system * @fmt: The text string to print @@ -682,6 +707,7 @@ void vpanic(const char *fmt, va_list args) sys_info(panic_print); + panic_notify_pre_kdump(buf); kmsg_dump_desc(KMSG_DUMP_PANIC, buf); /*
