Messages in this thread | | | Date | Thu, 9 May 2019 18:58:23 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..." |
| |
On (05/08/19 19:31), Tetsuo Handa wrote: [..] > 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.
Hmm... That's interesting...
[..] > +#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
I suppose this patch is for internal testing at Google only. I don't think we can consider upstreaming it.
> 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...
I thought that we have MSG_FORMAT_SYSLOG exactly for things like these, so you can look at actual message level <%d> and then decide if it's a warning or a false alarm.
These are pr_info() level messages, but the text contains "WARNING: "
[..] pvr2_trace(PVR2_TRACE_ERROR_LEGS, "WARNING: Detected a wedged cx25840 chip; the device will not work."); [..]
I would suggest to fix pvrusb2-i2c-core.c. I don't think we really want to $text =~ s/WARNING//g in printk.
-ss
| |