diff options
Diffstat (limited to 'kernel/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 55 |
1 files changed, 48 insertions, 7 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index e30107d216a5..fc3f8970eea2 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; @@ -483,6 +485,9 @@ static bool have_nbcon_console; */ bool have_boot_console; +/* See printk_legacy_allow_panic_sync() for details. */ +bool legacy_allow_panic_sync; + /* * Specifies if the console lock/unlock dance is needed for console * printing. If @have_boot_console is true, the nbcon consoles will @@ -2330,12 +2335,28 @@ out: return ret; } +/* + * 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 && !is_printk_legacy_deferred()) { + 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; + bool defer_legacy = false; int printed_len; - bool in_sched = false; /* Suppress unimportant messages after panic happens */ if (unlikely(suppress_printk)) @@ -2349,17 +2370,35 @@ asmlinkage int vprintk_emit(int facility, int level, if (other_cpu_in_panic() && !panic_triggering_all_cpu_backtrace) return 0; + /* If called from the scheduler, we can not call up(). */ if (level == LOGLEVEL_SCHED) { level = LOGLEVEL_DEFAULT; - in_sched = true; + defer_legacy = do_trylock_unlock; + 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) { + nbcon_atomic_flush_pending(); + + /* + * 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 and they are allowed to + * flush. + */ + if (this_cpu_in_panic() && !legacy_allow_panic_sync) { + do_trylock_unlock = false; + defer_legacy = false; + } + } + + if (do_trylock_unlock) { /* * The caller may be holding system-critical or * timing-sensitive locks. Disable preemption during @@ -2379,7 +2418,7 @@ asmlinkage int vprintk_emit(int facility, int level, preempt_enable(); } - if (in_sched && printing_via_unlock) + if (defer_legacy) defer_console_output(); else wake_up_klogd(); @@ -3292,7 +3331,9 @@ void console_flush_on_panic(enum con_flush_mode mode) if (!have_boot_console) nbcon_atomic_flush_pending(); - console_flush_all(false, &next_seq, &handover); + /* Flush legacy consoles once allowed, even when dangerous. */ + if (legacy_allow_panic_sync) + console_flush_all(false, &next_seq, &handover); } /* |