From: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
To: Petr Mladek <pmladek@suse.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org, Dmitry Safonov <dima@arista.com>,
Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles".
Date: Wed, 13 May 2020 21:59:23 +0900 [thread overview]
Message-ID: <2173e3ac-7d5e-24da-0c1e-6472df905767@i-love.sakura.ne.jp> (raw)
In-Reply-To: <20200513121942.GK17734@linux-b0ei>
On 2020/05/13 21:19, Petr Mladek wrote:
> On Wed 2020-05-13 20:24:24, Tetsuo Handa wrote:
>> On 2020/05/13 19:49, Michal Hocko wrote:
>>> On Wed 13-05-20 12:04:13, Petr Mladek wrote:
>>>> What is so special about OOM dump task so that it would deserve such
>>>> complications?
>
>> I don't think dump_tasks() is important information to be printed on consoles.
>> But since somebody might think dump_tasks() is important information to be
>> printed on consoles, I suggest switching KERN_NO_CONSOLES using e.g. sysctl.
>
> You might achieve the same with DEBUG loglevel. Or do I miss anything?
Use of KERN_DEBUG affects userspace syslog daemon. We will have to ask administrators
to configure syslog daemon not to filter KERN_DEBUG messages. And administrators will
be bothered by needless KERN_DEBUG messages. Also,
>
> [*] It will have no effect when it was disabled by a sysfs knob.
we will have to ask people to "don't make pr_debug() no-op" or
"use KERN_DEBUG instead of pr_debug()".
Your suggestion to change KERN_$LOGLEVEL keeps bothering people. That's bad.
> I know that it is meant as a modifier, like LOGLEVEL_SCHED and
> KERN_CONT.
Right. KERN_NO_CONSOLES is a modifier.
> But this is another reason to avoid it. We already have
> huge pain with these two modifiers. They both do not work well.
KERN_NO_CONSOLES can not cause pains like LOGLEVEL_SCHED because
KERN_NO_CONSOLES is to say "no need to call console drivers" while
LOGLEVEL_SCHED is to say "don't call console drivers now but have
to call console drivers later".
On 2020/05/13 21:34, Petr Mladek wrote:
> On Wed 2020-05-13 20:03:53, Tetsuo Handa wrote:
>> On 2020/05/13 19:04, Petr Mladek wrote:
>>>> What is wrong with adding NO_CONSOLES ?
>>>
>>> How does it differ from KERN_DEBUG? The debug messages:
>>>
>>> + can be disabled via sysfs
>>> + might reach console when this loglevel is enabled
>>
>> KERN_NO_CONSOLES is different from KERN_DEBUG in that KERN_NO_CONSOLES
>> itself does not affect userspace daemon's judgement (whether to filter
>> KERN_$LOGLEVEL messages).
>
> And that is the evil thing about it. It goes around the loglevel
> filtering.
>
> The administrator wants to decide what messages are important for him.
Right.
> NO_CONSOLES would mess with this decision. Some messages would suddenly
> get hidden on console but appear in userspace.
Wrong. Console loglevel is already hiding some messages.
> Users would need to
> investigate what the hell is happening. They would need to find the
> new sysfs knob to restore the expected behavior, etc.
That's part of deciding what messages are important for him, as well as
deciding what KERN_$LOGLEVEL messages are worth printing to consoles.
next prev parent reply other threads:[~2020-05-13 13:00 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-24 2:42 [PATCH] printk: Add loglevel for "do not print to consoles" Tetsuo Handa
2020-04-24 13:28 ` Steven Rostedt
2020-04-24 14:00 ` Tetsuo Handa
2020-04-24 14:31 ` Steven Rostedt
2020-04-24 15:28 ` Tetsuo Handa
2020-04-24 15:42 ` Steven Rostedt
2020-04-24 15:52 ` Dmitry Safonov
2020-04-24 16:10 ` Tetsuo Handa
2020-04-24 16:21 ` Steven Rostedt
2020-04-24 16:34 ` Tetsuo Handa
2020-04-25 0:46 ` Sergey Senozhatsky
2020-04-25 1:07 ` Tetsuo Handa
2020-04-27 6:21 ` Sergey Senozhatsky
2020-04-28 11:33 ` Tetsuo Handa
2020-04-28 12:18 ` Michal Hocko
2020-04-28 13:11 ` Tetsuo Handa
2020-04-28 15:45 ` Michal Hocko
2020-04-28 16:23 ` Tetsuo Handa
2020-04-29 14:21 ` Michal Hocko
2020-04-29 16:35 ` Tetsuo Handa
2020-05-13 6:26 ` Sergey Senozhatsky
2020-05-13 7:58 ` Tetsuo Handa
2020-05-13 10:04 ` Petr Mladek
2020-05-13 10:49 ` Michal Hocko
2020-05-13 11:24 ` Tetsuo Handa
2020-05-13 12:19 ` Petr Mladek
2020-05-13 12:59 ` Tetsuo Handa [this message]
2020-05-14 8:00 ` Petr Mladek
2020-05-14 11:23 ` Tetsuo Handa
2020-05-14 16:26 ` Petr Mladek
2020-05-14 23:24 ` Tetsuo Handa
2020-05-13 11:03 ` Tetsuo Handa
2020-05-13 12:34 ` Petr Mladek
2020-05-13 13:46 ` Steven Rostedt
2020-05-13 14:03 ` Tetsuo Handa
2020-05-13 13:55 ` Steven Rostedt
2020-05-13 15:20 ` Tetsuo Handa
2020-05-06 9:45 ` Tetsuo Handa
2020-05-06 15:26 ` Joe Perches
2020-05-07 0:50 ` Tetsuo Handa
2020-05-07 1:02 ` Joe Perches
2020-05-07 5:13 ` Tetsuo Handa
2020-05-07 5:30 ` Joe Perches
2020-05-07 5:39 ` Tetsuo Handa
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