diff --git a/include/linux/console.h b/include/linux/console.h index a8a25bd72bb7..827b16f0d5d5 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -465,10 +465,14 @@ static inline bool console_is_registered(const struct console *con) hlist_for_each_entry(con, &console_list, node) #ifdef CONFIG_PRINTK +extern void nbcon_cpu_emergency_enter(void); +extern void nbcon_cpu_emergency_exit(void); extern bool nbcon_can_proceed(struct nbcon_write_context *wctxt); extern bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt); extern bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt); #else +static inline void nbcon_cpu_emergency_enter(void) { } +static inline void nbcon_cpu_emergency_exit(void) { } static inline bool nbcon_can_proceed(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_enter_unsafe(struct nbcon_write_context *wctxt) { return false; } static inline bool nbcon_exit_unsafe(struct nbcon_write_context *wctxt) { return false; } diff --git a/include/linux/printk.h b/include/linux/printk.h index cf545b76131f..7a942e987b16 100644 --- a/include/linux/printk.h +++ b/include/linux/printk.h @@ -197,6 +197,7 @@ 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_acquire(struct uart_port *up); extern void nbcon_release(struct uart_port *up); void nbcon_atomic_flush_unsafe(void); @@ -280,6 +281,10 @@ static inline void printk_trigger_flush(void) { } +static inline void printk_legacy_allow_panic_sync(void) +{ +} + static inline void nbcon_acquire(struct uart_port *up) { } @@ -782,5 +787,3 @@ static inline void print_hex_dump_debug(const char *prefix_str, int prefix_type, print_hex_dump_debug(prefix_str, prefix_type, 16, 1, buf, len, true) #endif - -void printk_legacy_allow_panic_sync(void); diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c index 1c01f88d596d..c3ee245397f6 100644 --- a/kernel/printk/nbcon.c +++ b/kernel/printk/nbcon.c @@ -929,6 +929,29 @@ update_con: return nbcon_context_exit_unsafe(ctxt); } +/* Track the nbcon emergency nesting per CPU. */ +static DEFINE_PER_CPU(unsigned int, nbcon_pcpu_emergency_nesting); +static unsigned int early_nbcon_pcpu_emergency_nesting __initdata; + +/** + * nbcon_get_cpu_emergency_nesting - Get the per CPU emergency nesting pointer + * + * Return: Either a pointer to the per CPU emergency nesting counter of + * the current CPU or to the init data during early boot. + */ +static __ref unsigned int *nbcon_get_cpu_emergency_nesting(void) +{ + /* + * The value of __printk_percpu_data_ready gets set in normal + * context and before SMP initialization. As a result it could + * never change while inside an nbcon emergency section. + */ + if (!printk_percpu_data_ready()) + return &early_nbcon_pcpu_emergency_nesting; + + return this_cpu_ptr(&nbcon_pcpu_emergency_nesting); +} + /** * nbcon_atomic_emit_one - Print one record for an nbcon console using the * write_atomic() callback @@ -971,9 +994,15 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt) */ enum nbcon_prio nbcon_get_default_prio(void) { + unsigned int *cpu_emergency_nesting; + if (this_cpu_in_panic()) return NBCON_PRIO_PANIC; + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + if (*cpu_emergency_nesting) + return NBCON_PRIO_EMERGENCY; + return NBCON_PRIO_NORMAL; } @@ -1110,6 +1139,58 @@ void nbcon_atomic_flush_unsafe(void) __nbcon_atomic_flush_all(prb_next_reserve_seq(prb), true); } +/** + * nbcon_cpu_emergency_enter - Enter an emergency section where printk() + * messages for that CPU are only stored + * + * Upon exiting the emergency section, all stored messages are flushed. + * + * Context: Any context. Disables preemption. + * + * When within an emergency section, no printing occurs on that CPU. This + * is to allow all emergency messages to be dumped into the ringbuffer before + * flushing the ringbuffer. The actual printing occurs when exiting the + * outermost emergency section. + */ +void nbcon_cpu_emergency_enter(void) +{ + unsigned int *cpu_emergency_nesting; + + preempt_disable(); + + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + (*cpu_emergency_nesting)++; +} + +/** + * nbcon_cpu_emergency_exit - Exit an emergency section and flush the + * stored messages + * + * Flushing only occurs when exiting all nesting for the CPU. + * + * Context: Any context. Enables preemption. + */ +void nbcon_cpu_emergency_exit(void) +{ + unsigned int *cpu_emergency_nesting; + bool do_trigger_flush = false; + + cpu_emergency_nesting = nbcon_get_cpu_emergency_nesting(); + + WARN_ON_ONCE(*cpu_emergency_nesting == 0); + + if (*cpu_emergency_nesting == 1) + do_trigger_flush = true; + + /* Undo the nesting count of nbcon_cpu_emergency_enter(). */ + (*cpu_emergency_nesting)--; + + preempt_enable(); + + if (do_trigger_flush) + printk_trigger_flush(); +} + /** * nbcon_alloc - Allocate buffers needed by the nbcon console * @con: Console to allocate buffers for diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e8d60e29c17f..4a0df41d32b8 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2411,16 +2411,29 @@ asmlinkage int vprintk_emit(int facility, int level, * printing of all remaining records to all consoles so that * this context can return as soon as possible. Hopefully * another printk() caller will take over the printing. + * + * Also, nbcon_get_default_prio() requires migration disabled. */ preempt_disable(); + /* - * Try to acquire and then immediately release the console - * semaphore. The release will print out buffers. With the - * spinning variant, this context tries to take over the - * printing from another printing context. + * Do not emit for EMERGENCY priority. The console will be + * explicitly flushed when exiting the emergency section. */ - if (console_trylock_spinning()) - console_unlock(); + if (nbcon_get_default_prio() == NBCON_PRIO_EMERGENCY) { + do_trylock_unlock = false; + } else { + /* + * Try to acquire and then immediately release the + * console semaphore. The release will print out + * buffers. With the spinning variant, this context + * tries to take over the printing from another + * printing context. + */ + if (console_trylock_spinning()) + console_unlock(); + } + preempt_enable(); }