Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..."

From: Dmitry Vyukov <dvyukov@google.com>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	syzkaller <syzkaller@googlegroups.com>
Subject: Re: [syzbot? printk?] no WARN_ON() messages printed before "Kernel panic - not syncing: panic_on_warn set ..."
Date: Sat, 16 Mar 2019 16:10:15 +0100	[thread overview]
Message-ID: <CACT4Y+ay7nuT-7y2JARozV1s0VisuLdN6VT+w9OsEDs1PeBRoA@mail.gmail.com> (raw)
In-Reply-To: <2a48dee7-b649-65a4-be5d-8b3374013cee@i-love.sakura.ne.jp>

On Sat, Mar 16, 2019 at 4:02 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2019/03/16 23:57, Dmitry Vyukov wrote:
> > On Sat, Mar 16, 2019 at 3:53 PM Tetsuo Handa
> > <penguin-kernel@i-love.sakura.ne.jp> wrote:
> >>
> >> On 2019/03/16 23:16, Dmitry Vyukov wrote:
> >>>>> Maybe try running with "ignore_loglevel" kernel command line option added?
> >>>>
> >>>> Right, that's something I would expect 0-day and syzkaller to do.
> >>>
> >>> to double-check: enabling this won't lead to verbose/debug level of logging?
> >>>
> >>
> >> I don't know what "verbose/debug level" means. But enabling this option causes
> >> KERN_{EMERG,ALERT,CRIT,ERR,WARNING,NOTICE,INFO,DEBUG} be printed equally.
> >>
> >>   "ignore loglevel setting (prints all kernel messages to the console)"
> >>
> >> static bool suppress_message_printing(int level)
> >> {
> >>         return (level >= console_loglevel && !ignore_loglevel);
> >> }
> >
> > Then I don't think it's suitable: there will be too much output.
> >
>
> Then, we need to find what test is changing console_loglevel.
> Maybe add debug BUG_ON() in linux-next.git using CONFIG_DEBUG_AID_FOR_SYZBOT ?

Is there a single place to catch this? I could run syzkaller locally
first with the check.