linux-kernel - [PATCH v2] softlockup: serialized softlockup's log

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20231122100212.94327-1-lizhe.67@bytedance.com>
Date:   Wed, 22 Nov 2023 18:02:12 +0800
From:   lizhe.67@...edance.com
To:     dianders@...omium.org, akpm@...ux-foundation.org, pmladek@...e.com,
        lecopzer.chen@...iatek.com, kernelfans@...il.com
Cc:     linux-kernel@...r.kernel.org, lizefan.x@...edance.com,
        lizhe.67@...edance.com
Subject: [PATCH v2] softlockup: serialized softlockup's log

From: Li Zhe <lizhe.67@...edance.com>

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@...edance.com>
---
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