+ softlockup-serialized-softlockups-log.patch added to mm-nonmm-unstable branch

+ softlockup-serialized-softlockups-log.patch added to mm-nonmm-unstable branch

[Andrew Morton]

The patch titled
     Subject: softlockup: serialized softlockup's log
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     softlockup-serialized-softlockups-log.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/softlockup-serialized-softlockups-log.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Li Zhe <lizhe.67@bytedance.com>
Subject: softlockup: serialized softlockup's log
Date: Thu, 23 Nov 2023 16:40:22 +0800

If multiple CPUs trigger softlockup at the same time with
'softlockup_all_cpu_backtrace=0', the softlockup's logs will appear
staggeredly in dmesg, which will affect the viewing of the logs for
developer.  Since the code path for outputting softlockup logs is not a
kernel hotspot and the performance requirements for the code are not
strict, locks are used to serialize the softlockup log output to improve
the readability of the logs.

Link: https://lkml.kernel.org/r/20231123084022.10302-1-lizhe.67@bytedance.com
Signed-off-by: Li Zhe <lizhe.67@bytedance.com>
Cc: Douglas Anderson <dianders@chromium.org>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/watchdog.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/kernel/watchdog.c~softlockup-serialized-softlockups-log
+++ a/kernel/watchdog.c
@@ -448,6 +448,7 @@ static enum hrtimer_restart watchdog_tim
 	struct pt_regs *regs = get_irq_regs();
 	int duration;
 	int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace;
+	static DEFINE_SPINLOCK(watchdog_output_lock);
 
 	if (!watchdog_enabled)
 		return HRTIMER_NORESTART;
@@ -514,6 +515,7 @@ static enum hrtimer_restart watchdog_tim
 		/* Start period for the next softlockup warning. */
 		update_report_ts();
 
+		spin_lock(&watchdog_output_lock);
 		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
 			smp_processor_id(), duration,
 			current->comm, task_pid_nr(current));
@@ -523,6 +525,7 @@ static enum hrtimer_restart watchdog_tim
 			show_regs(regs);
 		else
 			dump_stack();
+		spin_unlock(&watchdog_output_lock);
 
 		if (softlockup_all_cpu_backtrace) {
 			trigger_allbutcpu_cpu_backtrace(smp_processor_id());
_

Patches currently in -mm which might be from lizhe.67@bytedance.com are

softlockup-serialized-softlockups-log.patch