linux-kernel - Re: [RFC] printk/sysrq: Don't play with console

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Message-ID: <90a22327-922d-6415-538a-6a3fcbe9f3e1@i-love.sakura.ne.jp>
Date:   Tue, 28 May 2019 17:02:56 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC] printk/sysrq: Don't play with console_loglevel

On 2019/05/28 13:22, Sergey Senozhatsky wrote:
> On (05/28/19 12:21), Tetsuo Handa wrote:
> [..]
>> What I suggested in my proposal ("printk: Introduce "store now but print later" prefix." at
>> https://lore.kernel.org/lkml/1550896930-12324-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp/T/#u )
>> is "whether the caller wants to defer printing to consoles regarding
>> this printk() call". And your suggestion is "whether the caller wants
>> to apply ignore_loglevel regarding this printk() call".
> 
> I'm not sure about "store now but print later" here. What Dmitry is
> talking about:
> 
>      bump console_loglevel on *this* particular CPU only,
>      not system-wide.
>      /* Which is implemented in a form of - all messages from this-CPU
>       * only should be printed regardless the loglevel, the rest should
>       * pass the usual suppress_message_printing() check. */

Dmitry's patch is changing only the header line (in other words, per printk() call).
Since op_p->handler(key) is out of KERN_UNSUPPRESSED effect, the body lines might
not be printed. I think that we need a way to pass KERN_UNSUPPRESSED from printk()
calls invoked from op_p->handler(key).

You are trying to omit passing KERN_UNSUPPRESSED by utilizing implicit printk
context information. But doesn't such attempt resemble find_printk_buffer() ?