diff --git a/include/linux/printk.h b/include/linux/printk.h index 866683a293af..2aa7c302d616 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -195,6 +195,7 @@ void show_regs_print_info(const char *log_lvl); extern asmlinkage void dump_stack_lvl(const char *log_lvl) __cold; extern asmlinkage void dump_stack(void) __cold; void printk_trigger_flush(void); +void printk_legacy_allow_panic_sync(void); extern void nbcon_driver_acquire(struct console *con); extern void nbcon_driver_release(struct console *con); void nbcon_atomic_flush_unsafe(void); @@ -278,6 +279,10 @@ static inline void printk_trigger_flush(void) { } +static inline void printk_legacy_allow_panic_sync(void) +{ +} + static inline void nbcon_driver_acquire(struct console *con) { } diff --git a/kernel/panic.c b/kernel/panic.c index c039f8e1ddae..de8115c829cf 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -364,6 +364,8 @@ void panic(const char *fmt, ...) panic_other_cpus_shutdown(_crash_kexec_post_notifiers); + printk_legacy_allow_panic_sync(); + /* * Run any panic handlers, including those that might need to * add information to the kmsg dump output. diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 76fd6d08e3df..5e887edfbaa5 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -471,7 +471,9 @@ static DEFINE_MUTEX(syslog_lock); static bool have_legacy_console; /* - * Specifies if an nbcon console is registered. + * Specifies if an nbcon console is registered. If nbcon consoles are present, + * synchronous printing of legacy consoles will not occur during panic until + * the backtrace has been stored to the ringbuffer. */ static bool have_nbcon_console; @@ -2341,12 +2343,29 @@ out: return ret; } +static bool legacy_allow_panic_sync; + +/* + * This acts as a one-way switch to allow legacy consoles to print from + * the printk() caller context on a panic CPU. It also attempts to flush + * the legacy consoles in this context. + */ +void printk_legacy_allow_panic_sync(void) +{ + legacy_allow_panic_sync = true; + + if (printing_via_unlock && !in_nmi()) { + if (console_trylock()) + console_unlock(); + } +} + asmlinkage int vprintk_emit(int facility, int level, const struct dev_printk_info *dev_info, const char *fmt, va_list args) { + bool do_trylock_unlock = printing_via_unlock; int printed_len; - bool in_sched = false; /* Suppress unimportant messages after panic happens */ if (unlikely(suppress_printk)) @@ -2362,15 +2381,42 @@ asmlinkage int vprintk_emit(int facility, int level, if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; - in_sched = true; + /* If called from the scheduler, we can not call up(). */ + do_trylock_unlock = false; } printk_delay(level); printed_len = vprintk_store(facility, level, dev_info, fmt, args); - /* If called from the scheduler, we can not call up(). */ - if (!in_sched && printing_via_unlock) { + if (have_nbcon_console && !have_boot_console) { + bool is_panic_context = this_cpu_in_panic(); + + /* + * In panic, the legacy consoles are not allowed to print from + * the printk calling context unless explicitly allowed. This + * gives the safe nbcon consoles a chance to print out all the + * panic messages first. This restriction only applies if + * there are nbcon consoles registered. + */ + if (is_panic_context) + do_trylock_unlock &= legacy_allow_panic_sync; + + /* + * There are situations where nbcon atomic printing should + * happen in the printk() caller context: + * + * - When this CPU is in panic. + * + * Note that if boot consoles are registered, the console + * lock/unlock dance must be relied upon instead because nbcon + * consoles cannot print simultaneously with boot consoles. + */ + if (is_panic_context) + nbcon_atomic_flush_pending(); + } + + if (do_trylock_unlock) { /* * The caller may be holding system-critical or * timing-sensitive locks. Disable preemption during @@ -2390,10 +2436,10 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - if (in_sched) - defer_console_output(); - else + if (do_trylock_unlock) wake_up_klogd(); + else + defer_console_output(); return printed_len; }