softlockup: serialized softlockup's log

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>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Cc: Lecopzer Chen <lecopzer.chen@mediatek.com>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: Zefan Li <lizefan.x@bytedance.com>
Cc: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 5cd6d4e269157973acecd00afc91646720fee2be..bf30a6fac66518b3bfd22ece7bea206f1292eefe 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -448,6 +448,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
        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_timer_fn(struct hrtimer *hrtimer)
                /* 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_timer_fn(struct hrtimer *hrtimer)
                        show_regs(regs);
                else
                        dump_stack();
+               spin_unlock(&watchdog_output_lock);
 
                if (softlockup_all_cpu_backtrace) {
                        trigger_allbutcpu_cpu_backtrace(smp_processor_id());