linux-kernel - Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic

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Message-ID: <20190509103623.GA3369@jagdpanzerIV>
Date:   Thu, 9 May 2019 19:36:23 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel
 panic - not syncing: panic_on_warn set ..."

On (05/09/19 19:26), Tetsuo Handa wrote:
> >> 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.
> 
> Since syzbot needs to use console output, message level is not available.

Sorry, not following. MSG_FORMAT_SYSLOG should add message level
to console output. Booting the kernel with console_msg_format=syslog
will change msg_print_text() behaviour, and you'll get on your serial
console messages in

	<print_syslog>[print_time][print_caller] message text\n

format.

Does this work for you?

	-ss