Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Wed, 3 Jun 2020 14:44:05 +0200
From:   Petr Mladek <pmladek@suse.com>
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzkaller <syzkaller@googlegroups.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: twist: allow disabling reboot request
Message-ID: <20200603124405.GA22497@linux-b0ei>
References: <e0d6c04f-7601-51e7-c969-300e938dedc0@i-love.sakura.ne.jp>
 <CAHk-=wgz=7MGxxX-tmMmdCsKyYJkuyxNc-4uLP=e_eEV=OzUaw@mail.gmail.com>
 <CAHk-=wjW+_pjJzVRMuCbLhbWLkvEQVYJoXVBYGNW2PUgtX1fDw@mail.gmail.com>
 <13b0a475-e70e-c490-d34d-0c7a34facf7c@i-love.sakura.ne.jp>
 <CAHk-=wjj9ooYACNvO2P_Gr_=aN0g=iEqtg0TwBJo18wbn4gthg@mail.gmail.com>
 <6116ed2e-cee1-d82f-6b68-ddb1bbb6abe2@i-love.sakura.ne.jp>
 <CAHk-=wiVQUo_RJAaivHU5MFdznNOX4GKgJH1xrFc83e9oLnuvQ@mail.gmail.com>
 <19d377d3-8037-8090-0f99-447f72cc1d8c@i-love.sakura.ne.jp>
 <38df9737-3c04-dca2-0df4-115a9c1634e5@i-love.sakura.ne.jp>
 <51eaa6cd-33ce-f9d8-942c-c797c0ec6733@i-love.sakura.ne.jp>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <51eaa6cd-33ce-f9d8-942c-c797c0ec6733@i-love.sakura.ne.jp>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed 2020-06-03 20:03:28, Tetsuo Handa wrote:
> On 2020/05/29 22:26, Tetsuo Handa wrote:
> >     By the way, I do worry that people forget to perform these steps when they do
> >     their tests without asking syzbot...
> 
> Here is a draft of boot-time switching. Since kconfig can handle string variable up to
> 2048 characters, we could hold the content of the "your-config" file inside .config file
> in order to avoid relying on external file in "syzkaller tree". But since only one kconfig
> option is used, basically the way to temporarily include/exclude specific options (under
> automated testing by syzbot) seems to remain directly patching apply_twist_flags(), for
> https://github.com/google/syzkaller/blob/master/dashboard/config/util.sh will automatically
> overwrite CONFIG_DEFAULT_TWIST_FLAGS settings. If each twist flag were using independent
> kconfig option, the way to temporarily include/exclude specific options will become directly
> patching Kconfig file.
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 82d91547d122..78fdbb4f17b1 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -1038,4 +1038,12 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { }
>  	 /* OTHER_WRITABLE?  Generally considered a bad idea. */		\
>  	 BUILD_BUG_ON_ZERO((perms) & 2) +					\
>  	 (perms))
> +
> +/* Flags for twisting kernel behavior. */
> +struct twist_flags {
> +	bool disable_kbd_k_spec_handler;
> +	bool disable_reboot_request;
> +};
> +extern struct twist_flags twist_flags;


Why all these options have to be in a single structure?


> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 498d344ea53a..41cfabc74ad7 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -2338,4 +2338,9 @@ config HYPERV_TESTING
>  
>  endmenu # "Kernel Testing and Coverage"
>  
> +menuconfig DEFAULT_TWIST_FLAGS
> +	string "Default twist options (DANGEROUS)"
> +	help
> +	  Don't specify anything unless you know what you are doing.
> +
>  endmenu # Kernel hacking

Why such a crazy build configure option?

I think that the only way to get this upstream is to:

   + Add separate boot options that might theoretically be used also
     by other people.

   + Use boot parameters and not build configuration.

   + Avoid the meaningless word "twist" !!!


Best Regards,
Petr