diff options
Diffstat (limited to 'kernel/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 101 |
1 files changed, 59 insertions, 42 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1c6e7dfc4ba7..b06f63e276c1 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -347,6 +347,29 @@ static bool panic_in_progress(void) return unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID); } +/* Return true if a panic is in progress on the current CPU. */ +bool this_cpu_in_panic(void) +{ + /* + * 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 unlikely(atomic_read(&panic_cpu) == raw_smp_processor_id()); +} + +/* + * 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) +{ + return (panic_in_progress() && !this_cpu_in_panic()); +} + /* * This is used for debugging the mess that is the VT code by * keeping track if we have the console semaphore held. It's @@ -439,12 +462,6 @@ static int console_msg_format = MSG_FORMAT_DEFAULT; static DEFINE_MUTEX(syslog_lock); #ifdef CONFIG_PRINTK -/* - * During panic, heavy printk by other CPUs can delay the - * panic and risk deadlock on console resources. - */ -static int __read_mostly suppress_panic_printk; - DECLARE_WAIT_QUEUE_HEAD(log_wait); /* All 3 protected by @syslog_lock. */ /* the next printk record to read by syslog(READ) or /proc/kmsg */ @@ -1835,10 +1852,23 @@ static bool console_waiter; */ static void console_lock_spinning_enable(void) { + /* + * Do not use spinning in panic(). The panic CPU wants to keep the lock. + * Non-panic CPUs abandon the flush anyway. + * + * Just keep the lockdep annotation. The panic-CPU should avoid + * taking console_owner_lock because it might cause a deadlock. + * This looks like the easiest way how to prevent false lockdep + * reports without handling races a lockless way. + */ + if (panic_in_progress()) + goto lockdep; + raw_spin_lock(&console_owner_lock); console_owner = current; raw_spin_unlock(&console_owner_lock); +lockdep: /* The waiter may spin on us after setting console_owner */ spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); } @@ -1863,6 +1893,22 @@ static int console_lock_spinning_disable_and_check(int cookie) { int waiter; + /* + * Ignore spinning waiters during panic() because they might get stopped + * or blocked at any time, + * + * It is safe because nobody is allowed to start spinning during panic + * in the first place. If there has been a waiter then non panic CPUs + * might stay spinning. They would get stopped anyway. The panic context + * will never start spinning and an interrupted spin on panic CPU will + * never continue. + */ + if (panic_in_progress()) { + /* Keep lockdep happy. */ + spin_release(&console_owner_dep_map, _THIS_IP_); + return 0; + } + raw_spin_lock(&console_owner_lock); waiter = READ_ONCE(console_waiter); console_owner = NULL; @@ -2259,8 +2305,12 @@ asmlinkage int vprintk_emit(int facility, int level, if (unlikely(suppress_printk)) return 0; - if (unlikely(suppress_panic_printk) && - atomic_read(&panic_cpu) != raw_smp_processor_id()) + /* + * The messages on the panic CPU are the most important. If + * non-panic CPUs are generating any messages, they will be + * silently dropped. + */ + if (other_cpu_in_panic()) return 0; if (level == LOGLEVEL_SCHED) { @@ -2590,26 +2640,6 @@ 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 * @@ -2765,8 +2795,6 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped) bool printk_get_next_message(struct printk_message *pmsg, u64 seq, bool is_extended, bool may_suppress) { - static int panic_console_dropped; - struct printk_buffers *pbufs = pmsg->pbufs; const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf); const size_t outbuf_sz = sizeof(pbufs->outbuf); @@ -2794,17 +2822,6 @@ bool printk_get_next_message(struct printk_message *pmsg, u64 seq, pmsg->seq = r.info->seq; pmsg->dropped = r.info->seq - seq; - /* - * Check for dropped messages in panic here so that printk - * suppression can occur as early as possible if necessary. - */ - if (pmsg->dropped && - panic_in_progress() && - panic_console_dropped++ > 10) { - suppress_panic_printk = 1; - pr_warn_once("Too many dropped messages. Suppress messages on non-panic CPUs to prevent livelock.\n"); - } - /* Skip record that has level above the console loglevel. */ if (may_suppress && suppress_message_printing(r.info->level)) goto out; @@ -3750,7 +3767,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre might_sleep(); - seq = prb_next_seq(prb); + seq = prb_next_reserve_seq(prb); /* Flush the consoles so that records up to @seq are printed. */ console_lock(); |