Messages in this thread Patch in this message | | | From | Tetsuo Handa <> | Subject | Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..." | Date | Wed, 8 May 2019 19:31:06 +0900 |
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Hello.
We are again getting corrupted reports where message from WARN() is missing. For example, https://syzkaller.appspot.com/text?tag=CrashLog&x=1720cac8a00000 was titled as "WARNING in cgroup_exit" because the "WARNING: CPU: 0 PID: 7870 at kernel/cgroup/cgroup.c:6008 cgroup_exit+0x51a/0x5d0" line is there but https://syzkaller.appspot.com/text?tag=CrashLog&x=1670a602a00000 was titled as "corrupted report (2)" because the "WARNING: CPU: 0 PID: 10223 at kernel/cgroup/cgroup.c:6008 cgroup_exit+0x51a/0x5d0" line is missing. Also, it is unlikely that there was no printk() for a few minutes. Thus, I suspect something is again suppressing console output. Since this problem is happening in 5.1.0-next-20190507, do we want to try below one?
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
By the way, recently we are hitting false positives caused by "WARNING:" string from not WARN() messages but plain printk() messages (e.g.
https://syzkaller.appspot.com/bug?id=31bdef63e48688854fde93e6edf390922b70f8a4 https://syzkaller.appspot.com/bug?id=faae4720a75cadb8cd0dbda5c4d3542228d37340
) and we need to avoid emitting "WARNING:" string from plain printk() messages during fuzzing testing. I guess we want to add something like CONFIG_DEBUG_AID_FOR_SYZBOT to all kernels in order to mask such string...
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