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

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Message-ID: <2a48dee7-b649-65a4-be5d-8b3374013cee@i-love.sakura.ne.jp>
Date:   Sun, 17 Mar 2019 00:02:28 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.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 2019/03/16 23:57, Dmitry Vyukov wrote:
> On Sat, Mar 16, 2019 at 3:53 PM Tetsuo Handa
> <penguin-kernel@...ove.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 ?