linux-kernel - Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

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Date:   Tue, 17 Dec 2019 17:24:49 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

On (19/12/17 08:54), Dmitry Vyukov wrote:
> On Tue, Dec 17, 2019 at 6:12 AM Sergey Senozhatsky
> <sergey.senozhatsky.work@...il.com> wrote:
> >
> > On (19/12/16 18:59), Tetsuo Handa wrote:
> >
> > Can you fuzz test with `ignore_loglevel'?
> 
> We can set ignore_loglevel in syzbot configs, but won't it then print
> everything including verbose debug output?

What would be the most active source of debug output?

dev_dbg(), which is dev_printk(KERN_DEBUG), can be compiled out, if I'm
not mistaken. It probably depends on CONFIG_DEBUG or something similar,
unlike dev_printk(), which depends on CONFIG_PRINTK. It seems that we have
significantly more dev_dbg() users, than direct dev_printk(KERN_DEBUG).

Does fuzz tester hit pr_debug() often? File systems? Some of them
have ways to compile out debugging output as well. E.g. jbd_debug,
_debug, ext4_debug, and so on.

	-ss