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* [PATCH] printk: Monitor change of console loglevel.
@ 2019-05-10 15:19 Tetsuo Handa
  2019-05-14  9:19 ` Sergey Senozhatsky
  2019-05-24 17:17 ` Linus Torvalds
  0 siblings, 2 replies; 11+ messages in thread
From: Tetsuo Handa @ 2019-05-10 15:19 UTC (permalink / raw)
  To: Andrew Morton
  Cc: linux-kernel, Tetsuo Handa, Dmitry Vyukov, Petr Mladek,
	Sergey Senozhatsky

We are seeing syzbot reports [1] where printk() messages prior to panic()
are missing for unknown reason. To test whether it is due to some testcase
changing console loglevel, let's panic() as soon as console loglevel has
changed. This patch is intended for testing on linux-next.git only, and
will be removed after we found what is wrong.

[1] https://lkml.kernel.org/r/127c9c3b-f878-174f-7065-66dc50fcabcf@i-love.sakura.ne.jp

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e1e8250..f0b9463 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3338,3 +3338,23 @@ void kmsg_dump_rewind(struct kmsg_dumper *dumper)
 EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
 
 #endif
+
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+static int initial_loglevel;
+static void check_loglevel(struct timer_list *timer)
+{
+	if (console_loglevel < initial_loglevel)
+		panic("Console loglevel changed (%d->%d)!", initial_loglevel,
+		      console_loglevel);
+	mod_timer(timer, jiffies + HZ);
+}
+static int __init loglevelcheck_init(void)
+{
+	static DEFINE_TIMER(timer, check_loglevel);
+
+	initial_loglevel = console_loglevel;
+	mod_timer(&timer, jiffies + HZ);
+	return 0;
+}
+late_initcall(loglevelcheck_init);
+#endif
-- 
1.8.3.1

^ permalink raw reply	[flat|nested] 11+ messages in thread

end of thread, other threads:[~2019-05-25  0:56 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-10 15:19 [PATCH] printk: Monitor change of console loglevel Tetsuo Handa
2019-05-14  9:19 ` Sergey Senozhatsky
2019-05-15 14:32   ` Tetsuo Handa
2019-05-23  9:56     ` Tetsuo Handa
2019-05-24  7:55       ` Dmitry Vyukov
2019-05-24 10:35         ` Tetsuo Handa
2019-05-24 17:17 ` Linus Torvalds
2019-05-24 17:40   ` Joe Perches
2019-05-24 17:55     ` Linus Torvalds
2019-05-25  0:14   ` Tetsuo Handa
2019-05-25  0:56     ` Joe Perches

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