From: John Ogness john.ogness@linutronix.de
[ Upstream commit 779dbc2e78d746250f07c463e13ac603b349f6f3 ]
Commit 13fb0f74d702 ("printk: Avoid livelock with heavy printk during panic") introduced a mechanism to silence non-panic CPUs if too many messages are being dropped. Aside from trying to workaround the livelock bugs of legacy consoles, it was also intended to avoid losing panic messages. However, if non-panic CPUs are writing to the ringbuffer, then reacting to dropped messages is too late.
Another motivation is that non-finalized messages already might be skipped in panic(). In other words, random messages from non-panic CPUs might already get lost. It is better to ignore all to avoid confusion.
To avoid losing panic CPU messages, silence non-panic CPUs immediately on panic.
Signed-off-by: John Ogness john.ogness@linutronix.de Reviewed-by: Petr Mladek pmladek@suse.com Link: https://lore.kernel.org/r/20240207134103.1357162-13-john.ogness@linutronix.d... Signed-off-by: Petr Mladek pmladek@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/printk/printk.c | 26 ++++++-------------------- 1 file changed, 6 insertions(+), 20 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 742fb479b1d60..336c092632f4e 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -462,12 +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 */ @@ -2293,7 +2287,12 @@ asmlinkage int vprintk_emit(int facility, int level, if (unlikely(suppress_printk)) return 0;
- if (unlikely(suppress_panic_printk) && other_cpu_in_panic()) + /* + * 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) { @@ -2778,8 +2777,6 @@ 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); @@ -2807,17 +2804,6 @@ 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;