Subject: [PATCH 18/24] kernel/panic: Add atomic write enforcement to warn/panic
From: Thomas Gleixner <[email-masked]>
Date: Sun, 11 Sep 2022 00:28:17 +0200

Invoke the atomic write enforcement functions for warn/panic to
ensure that the information gets out to the consoles.

For the panic case, add explicit intermediate atomic flush calls to
ensure immediate flushing at important points. Otherwise the atomic
flushing only occurs when dropping out of the elevated priority,
which for panic may never happen.

It is important to note that if there are any legacy consoles
registered, they will be attempting to directly print from the
printk-caller context, which may jeopardize the reliability of the
atomic consoles. Optimally there should be no legacy consoles
registered.

Co-developed-by: John Ogness <[email-masked]>
Signed-off-by: John Ogness <[email-masked]>
Signed-off-by: Thomas Gleixner (Intel) <[email-masked]>
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/panic.c |   17 +++++++++++++++++
 1 file changed, 17 insertions(+)

Index: linux-6.3.0-rt11/kernel/panic.c
===================================================================
--- linux-6.3.0-rt11.orig/kernel/panic.c
+++ linux-6.3.0-rt11/kernel/panic.c
@@ -275,6 +275,7 @@ static void panic_other_cpus_shutdown(bo
  */
 void panic(const char *fmt, ...)
 {
+	enum cons_prio prev_prio;
 	static char buf[1024];
 	va_list args;
 	long i, i_next = 0, len;
@@ -322,6 +323,8 @@ void panic(const char *fmt, ...)
 	if (old_cpu != PANIC_CPU_INVALID && old_cpu != this_cpu)
 		panic_smp_self_stop();
 
+	prev_prio = cons_atomic_enter(CONS_PRIO_PANIC);
+
 	console_verbose();
 	bust_spinlocks(1);
 	va_start(args, fmt);
@@ -382,6 +385,8 @@ void panic(const char *fmt, ...)
 	if (_crash_kexec_post_notifiers)
 		__crash_kexec(NULL);
 
+	cons_atomic_flush(NULL, true);
+
 	console_unblank();
 
 	/*
@@ -406,6 +411,7 @@ void panic(const char *fmt, ...)
 		 * We can't use the "normal" timers since we just panicked.
 		 */
 		pr_emerg("Rebooting in %d seconds..\n", panic_timeout);
+		cons_atomic_flush(NULL, true);
 
 		for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) {
 			touch_nmi_watchdog();
@@ -424,6 +430,7 @@ void panic(const char *fmt, ...)
 		 */
 		if (panic_reboot_mode != REBOOT_UNDEFINED)
 			reboot_mode = panic_reboot_mode;
+		cons_atomic_flush(NULL, true);
 		emergency_restart();
 	}
 #ifdef __sparc__
@@ -436,12 +443,16 @@ void panic(const char *fmt, ...)
 	}
 #endif
 #if defined(CONFIG_S390)
+	cons_atomic_flush(NULL, true);
 	disabled_wait();
 #endif
 	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
 
 	/* Do not scroll important messages printed above */
 	suppress_printk = 1;
+
+	cons_atomic_exit(CONS_PRIO_PANIC, prev_prio);
+
 	local_irq_enable();
 	for (i = 0; ; i += PANIC_TIMER_STEP) {
 		touch_softlockup_watchdog();
@@ -652,6 +663,10 @@ struct warn_args {
 void __warn(const char *file, int line, void *caller, unsigned taint,
 	    struct pt_regs *regs, struct warn_args *args)
 {
+	enum cons_prio prev_prio;
+
+	prev_prio = cons_atomic_enter(CONS_PRIO_EMERGENCY);
+
 	disable_trace_on_warning();
 
 	if (file)
@@ -682,6 +697,8 @@ void __warn(const char *file, int line,
 
 	/* Just a warning, don't kill lockdep. */
 	add_taint(taint, LOCKDEP_STILL_OK);
+
+	cons_atomic_exit(CONS_PRIO_EMERGENCY, prev_prio);
 }
 
 #ifndef __WARN_FLAGS