diff options
Diffstat (limited to 'kernel/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 215 |
1 files changed, 149 insertions, 66 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 357a4d18f638..96fc38cb2e84 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -88,7 +88,7 @@ EXPORT_SYMBOL(oops_in_progress); static DEFINE_MUTEX(console_mutex); /* - * console_sem protects updates to console->seq and console_suspended, + * console_sem protects updates to console->seq * and also provides serialization for console printing. */ static DEFINE_SEMAPHORE(console_sem, 1); @@ -361,7 +361,7 @@ static bool panic_in_progress(void) * paths in the console code where we end up in places I want * locked without the console semaphore held). */ -static int console_locked, console_suspended; +static int console_locked; /* * Array of consoles built from command line options (console=) @@ -538,12 +538,14 @@ char *log_buf_addr_get(void) { return log_buf; } +EXPORT_SYMBOL_GPL(log_buf_addr_get); /* Return log buffer size */ u32 log_buf_len_get(void) { return log_buf_len; } +EXPORT_SYMBOL_GPL(log_buf_len_get); /* * Define how much of the log buffer we could take at maximum. The value @@ -2308,7 +2310,11 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - wake_up_klogd(); + if (in_sched) + defer_console_output(); + else + wake_up_klogd(); + return printed_len; } EXPORT_SYMBOL(vprintk_emit); @@ -2547,22 +2553,46 @@ MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to hig */ void suspend_console(void) { + struct console *con; + if (!console_suspend_enabled) return; pr_info("Suspending console(s) (use no_console_suspend to debug)\n"); pr_flush(1000, true); - console_lock(); - console_suspended = 1; - up_console_sem(); + + console_list_lock(); + for_each_console(con) + console_srcu_write_flags(con, con->flags | CON_SUSPENDED); + console_list_unlock(); + + /* + * Ensure that all SRCU list walks have completed. All printing + * contexts must be able to see that they are suspended so that it + * is guaranteed that all printing has stopped when this function + * completes. + */ + synchronize_srcu(&console_srcu); } void resume_console(void) { + struct console *con; + if (!console_suspend_enabled) return; - down_console_sem(); - console_suspended = 0; - console_unlock(); + + console_list_lock(); + for_each_console(con) + console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED); + console_list_unlock(); + + /* + * Ensure that all SRCU list walks have completed. All printing + * contexts must be able to see they are no longer suspended so + * that they are guaranteed to wake up and resume printing. + */ + synchronize_srcu(&console_srcu); + pr_flush(1000, true); } @@ -2585,6 +2615,26 @@ static int console_cpu_notify(unsigned int cpu) return 0; } +/* + * Return true if a panic is in progress on a remote CPU. + * + * On true, the local CPU should immediately release any printing resources + * that may be needed by the panic CPU. + */ +bool other_cpu_in_panic(void) +{ + if (!panic_in_progress()) + return false; + + /* + * We can use raw_smp_processor_id() here because it is impossible for + * the task to be migrated to the panic_cpu, or away from it. If + * panic_cpu has already been set, and we're not currently executing on + * that CPU, then we never will be. + */ + return atomic_read(&panic_cpu) != raw_smp_processor_id(); +} + /** * console_lock - block the console subsystem from printing * @@ -2597,9 +2647,11 @@ void console_lock(void) { might_sleep(); + /* On panic, the console_lock must be left to the panic cpu. */ + while (other_cpu_in_panic()) + msleep(1000); + down_console_sem(); - if (console_suspended) - return; console_locked = 1; console_may_schedule = 1; } @@ -2615,12 +2667,11 @@ EXPORT_SYMBOL(console_lock); */ int console_trylock(void) { - if (down_trylock_console_sem()) + /* On panic, the console_lock must be left to the panic cpu. */ + if (other_cpu_in_panic()) return 0; - if (console_suspended) { - up_console_sem(); + if (down_trylock_console_sem()) return 0; - } console_locked = 1; console_may_schedule = 0; return 1; @@ -2634,25 +2685,6 @@ int is_console_locked(void) EXPORT_SYMBOL(is_console_locked); /* - * Return true when this CPU should unlock console_sem without pushing all - * messages to the console. This reduces the chance that the console is - * locked when the panic CPU tries to use it. - */ -static bool abandon_console_lock_in_panic(void) -{ - if (!panic_in_progress()) - return false; - - /* - * We can use raw_smp_processor_id() here because it is impossible for - * the task to be migrated to the panic_cpu, or away from it. If - * panic_cpu has already been set, and we're not currently executing on - * that CPU, then we never will be. - */ - return atomic_read(&panic_cpu) != raw_smp_processor_id(); -} - -/* * Check if the given console is currently capable and allowed to print * records. * @@ -2665,6 +2697,9 @@ static inline bool console_is_usable(struct console *con) if (!(flags & CON_ENABLED)) return false; + if ((flags & CON_SUSPENDED)) + return false; + if (!con->write) return false; @@ -2948,7 +2983,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove any_progress = true; /* Allow panic_cpu to take over the consoles safely. */ - if (abandon_console_lock_in_panic()) + if (other_cpu_in_panic()) goto abandon; if (do_cond_resched) @@ -2983,11 +3018,6 @@ void console_unlock(void) bool flushed; u64 next_seq; - if (console_suspended) { - up_console_sem(); - return; - } - /* * Console drivers are called with interrupts disabled, so * @console_may_schedule should be cleared before; however, we may @@ -3045,10 +3075,28 @@ EXPORT_SYMBOL(console_conditional_schedule); void console_unblank(void) { + bool found_unblank = false; struct console *c; int cookie; /* + * First check if there are any consoles implementing the unblank() + * callback. If not, there is no reason to continue and take the + * console lock, which in particular can be dangerous if + * @oops_in_progress is set. + */ + cookie = console_srcu_read_lock(); + for_each_console_srcu(c) { + if ((console_srcu_read_flags(c) & CON_ENABLED) && c->unblank) { + found_unblank = true; + break; + } + } + console_srcu_read_unlock(cookie); + if (!found_unblank) + return; + + /* * Stop console printing because the unblank() callback may * assume the console is not within its write() callback. * @@ -3056,6 +3104,16 @@ void console_unblank(void) * In that case, attempt a trylock as best-effort. */ if (oops_in_progress) { + /* Semaphores are not NMI-safe. */ + if (in_nmi()) + return; + + /* + * Attempting to trylock the console lock can deadlock + * if another CPU was stopped while modifying the + * semaphore. "Hope and pray" that this is not the + * current situation. + */ if (down_trylock_console_sem() != 0) return; } else @@ -3085,14 +3143,24 @@ void console_unblank(void) */ void console_flush_on_panic(enum con_flush_mode mode) { + bool handover; + u64 next_seq; + /* - * If someone else is holding the console lock, trylock will fail - * and may_schedule may be set. Ignore and proceed to unlock so - * that messages are flushed out. As this can be called from any - * context and we don't want to get preempted while flushing, - * ensure may_schedule is cleared. + * Ignore the console lock and flush out the messages. Attempting a + * trylock would not be useful because: + * + * - if it is contended, it must be ignored anyway + * - console_lock() and console_trylock() block and fail + * respectively in panic for non-panic CPUs + * - semaphores are not NMI-safe + */ + + /* + * If another context is holding the console lock, + * @console_may_schedule might be set. Clear it so that + * this context does not call cond_resched() while flushing. */ - console_trylock(); console_may_schedule = 0; if (mode == CONSOLE_REPLAY_ALL) { @@ -3105,15 +3173,15 @@ void console_flush_on_panic(enum con_flush_mode mode) cookie = console_srcu_read_lock(); for_each_console_srcu(c) { /* - * If the above console_trylock() failed, this is an - * unsynchronized assignment. But in that case, the + * This is an unsynchronized assignment, but the * kernel is in "hope and pray" mode anyway. */ c->seq = seq; } console_srcu_read_unlock(cookie); } - console_unlock(); + + console_flush_all(false, &next_seq, &handover); } /* @@ -3679,8 +3747,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre /* * Hold the console_lock to guarantee safe access to - * console->seq and to prevent changes to @console_suspended - * until all consoles have been processed. + * console->seq. */ console_lock(); @@ -3688,6 +3755,11 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre for_each_console_srcu(c) { if (con && con != c) continue; + /* + * If consoles are not usable, it cannot be expected + * that they make forward progress, so only increment + * @diff for usable consoles. + */ if (!console_is_usable(c)) continue; printk_seq = c->seq; @@ -3696,18 +3768,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre } console_srcu_read_unlock(cookie); - /* - * If consoles are suspended, it cannot be expected that they - * make forward progress, so timeout immediately. @diff is - * still used to return a valid flush status. - */ - if (console_suspended) - remaining = 0; - else if (diff != last_diff && reset_on_progress) + if (diff != last_diff && reset_on_progress) remaining = timeout_ms; console_unlock(); + /* Note: @diff is 0 if there are no usable consoles. */ if (diff == 0 || remaining == 0) break; @@ -3741,7 +3807,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre * printer has been seen to make some forward progress. * * Context: Process context. May sleep while acquiring console lock. - * Return: true if all enabled printers are caught up. + * Return: true if all usable printers are caught up. */ static bool pr_flush(int timeout_ms, bool reset_on_progress) { @@ -3798,11 +3864,33 @@ static void __wake_up_klogd(int val) preempt_enable(); } +/** + * wake_up_klogd - Wake kernel logging daemon + * + * Use this function when new records have been added to the ringbuffer + * and the console printing of those records has already occurred or is + * known to be handled by some other context. This function will only + * wake the logging daemon. + * + * Context: Any context. + */ void wake_up_klogd(void) { __wake_up_klogd(PRINTK_PENDING_WAKEUP); } +/** + * defer_console_output - Wake kernel logging daemon and trigger + * console printing in a deferred context + * + * Use this function when new records have been added to the ringbuffer, + * this context is responsible for console printing those records, but + * the current context is not allowed to perform the console printing. + * Trigger an irq_work context to perform the console printing. This + * function also wakes the logging daemon. + * + * Context: Any context. + */ void defer_console_output(void) { /* @@ -3819,12 +3907,7 @@ void printk_trigger_flush(void) int vprintk_deferred(const char *fmt, va_list args) { - int r; - - r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); - defer_console_output(); - - return r; + return vprintk_emit(0, LOGLEVEL_SCHED, NULL, fmt, args); } int _printk_deferred(const char *fmt, ...) |