linux-kernel - Re: Can printk() sleep at runtime?

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Date:   Fri, 1 Jun 2018 11:30:01 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        SergeySenozhatsky <sergey.senozhatsky@...il.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jonathan Corbet <corbet@....net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Michael Turquette <mturquette@...libre.com>
Subject: Re: Can printk() sleep at runtime?

Hi Jia-Ju,

On Fri, Jun 1, 2018 at 2:59 AM, Jia-Ju Bai <baijiaju1990@...il.com> wrote:
> On 2018/6/1 5:13, Steven Rostedt wrote:
>> On Thu, 31 May 2018 18:42:48 +0200
>> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>> On Thu, May 31, 2018 at 5:19 PM, Stephen Boyd <sboyd@...nel.org> wrote:
>>>> Quoting Linus Torvalds (2018-05-31 07:32:10)
>>>>> On Thu, May 31, 2018 at 5:05 AM Petr Mladek <pmladek@...e.com> wrote:
>>>>>>
>>>>>> Anyway, we need to fix or remove this format. vsprintf-like functions
>>>>>> are called in any context and nobody expect that they might sleep.
>>>>>
>>>>> Ack. I guess the argument is that "%pCr" is rare, and none of *those*
>>>>> users may care, but I do think that doing things wrong as-is.
>>>>>
>>>>> It's too subtle to have to know you're in a particular locking context
>>>>> when you use a particular %p modifier.
>>>>
>>>> Agreed. Removing the format seems to be the best approach. It looks like
>>>> only Geert has used it in the last few years and it hasn't been used
>>>> much otherwise.
>>>
>>> Indeed, just 3 users (the broadcom one isn't mine):
>>>      drivers/clk/renesas/renesas-cpg-mssr.c
>>>      drivers/thermal/broadcom/bcm2835_thermal.c
>>>      drivers/tty/serial/sh-sci.c
>>>
>>> Alternatively, can we have a special version __clk_get_rate() that just
>>> returns clk->core->rate?
>>> Or would that be too inaccurate in the presence of CLK_GET_RATE_NOCACHE?
>>> The function could still return 0 in case the flag is set.
>>
>> If it's only used in three locations, I think it would be better to
>> simply remove it from vsprintf() and have the three callers call
>> clk_get_rate() directly.

OK, patches sent.

Thanks for reporting!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds