[PATCH v2] softlockup: serialized softlockup's log

From: lizhe . 67
Date: Wed Nov 22 2023 - 05:03:09 EST


From: Li Zhe <lizhe.67@xxxxxxxxxxxxx>

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.

Signed-off-by: Li Zhe <lizhe.67@xxxxxxxxxxxxx>
---
Changelogs:

v1->v2:
- define the lock outside the scope of function
- add precondition 'softlockup_all_cpu_backtrace=0' in commit message

kernel/watchdog.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 5cd6d4e26915..6c80dd8ff24b 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -28,6 +28,8 @@
#include <linux/kvm_para.h>

static DEFINE_MUTEX(watchdog_mutex);
+/* This lock is used to prevent concurrent actions of softlockup output logs */
+static DEFINE_SPINLOCK(watchdog_output_lock);

#if defined(CONFIG_HARDLOCKUP_DETECTOR) || defined(CONFIG_HARDLOCKUP_DETECTOR_SPARC64)
# define WATCHDOG_HARDLOCKUP_DEFAULT 1
@@ -514,6 +516,7 @@ 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 +526,7 @@ 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());
--
2.20.1