diff options
Diffstat (limited to 'debian/patches-rt/0003-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch')
| -rw-r--r-- | debian/patches-rt/0003-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/debian/patches-rt/0003-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch b/debian/patches-rt/0003-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch new file mode 100644 index 000000000..d7575e9a5 --- /dev/null +++ b/debian/patches-rt/0003-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch @@ -0,0 +1,86 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Wed, 7 Feb 2024 14:47:01 +0106 +Subject: [PATCH 03/48] printk: Avoid non-panic CPUs writing to ringbuffer +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz + +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.de +Signed-off-by: Petr Mladek <pmladek@suse.com> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/printk.c | 26 ++++++-------------------- + 1 file changed, 6 insertions(+), 20 deletions(-) + +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -462,12 +462,6 @@ static int console_msg_format = MSG_FORM + 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 */ +@@ -2322,7 +2316,12 @@ asmlinkage int vprintk_emit(int facility + 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) { +@@ -2807,8 +2806,6 @@ void console_prepend_dropped(struct prin + 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); +@@ -2836,17 +2833,6 @@ bool printk_get_next_message(struct prin + 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; |