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

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Message-ID: <CAMuHMdWbwQ3GKovGGjMv+uWdJBoLYgXHAFj53qLcK1PjHg=0Gg@mail.gmail.com>
Date:   Thu, 31 May 2018 18:42:48 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Stephen Boyd <sboyd@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Petr Mladek <pmladek@...e.com>, baijiaju1990@...il.com,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        SergeySenozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        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 Stephen,

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.

Thanks!

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