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-rw-r--r--debian/patches-rt/0097-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch78
1 files changed, 78 insertions, 0 deletions
diff --git a/debian/patches-rt/0097-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch b/debian/patches-rt/0097-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch
new file mode 100644
index 0000000000..2f5a4ba17d
--- /dev/null
+++ b/debian/patches-rt/0097-printk-Avoid-non-panic-CPUs-writing-to-ringbuffer.patch
@@ -0,0 +1,78 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Fri, 20 Oct 2023 09:37:05 +0000
+Subject: [PATCH 097/134] printk: Avoid non-panic CPUs writing to ringbuffer
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.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.
+
+To avoid losing panic CPU messages, silence non-panic CPUs
+immediately on panic.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+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 */
+@@ -2323,7 +2317,12 @@ 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) {
+@@ -2800,8 +2799,6 @@ 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);
+@@ -2829,17 +2826,6 @@ 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;