linux-kernel - [PATCH printk v2 08/11] panic: Add atomic write enforcement to warn/panic

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Date:   Wed, 20 Sep 2023 01:14:53 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Arnd Bergmann <arnd@...db.de>
Subject: [PATCH printk v2 08/11] panic: Add atomic write enforcement to warn/panic

From: Thomas Gleixner <tglx@...utronix.de>

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 <john.ogness@...utronix.de>
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Signed-off-by: Thomas Gleixner (Intel) <tglx@...utronix.de>
---
 kernel/panic.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/kernel/panic.c b/kernel/panic.c
index 07239d4ad81e..86ed71ba8c4d 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -275,6 +275,7 @@ static void panic_other_cpus_shutdown(bool crash_kexec)
  */
 void panic(const char *fmt, ...)
 {
+	enum nbcon_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 = nbcon_atomic_enter(NBCON_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);
 
+	nbcon_atomic_flush_all();
+
 	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);
+		nbcon_atomic_flush_all();
 
 		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;
+		nbcon_atomic_flush_all();
 		emergency_restart();
 	}
 #ifdef __sparc__
@@ -436,12 +443,16 @@ void panic(const char *fmt, ...)
 	}
 #endif
 #if defined(CONFIG_S390)
+	nbcon_atomic_flush_all();
 	disabled_wait();
 #endif
 	pr_emerg("---[ end Kernel panic - not syncing: %s ]---\n", buf);
 
 	/* Do not scroll important messages printed above */
 	suppress_printk = 1;
+
+	nbcon_atomic_exit(NBCON_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 nbcon_prio prev_prio;
+
+	prev_prio = nbcon_atomic_enter(NBCON_PRIO_EMERGENCY);
+
 	disable_trace_on_warning();
 
 	if (file)
@@ -682,6 +697,8 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 
 	/* Just a warning, don't kill lockdep. */
 	add_taint(taint, LOCKDEP_STILL_OK);
+
+	nbcon_atomic_exit(NBCON_PRIO_EMERGENCY, prev_prio);
 }
 
 #ifdef CONFIG_BUG
-- 
2.39.2