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Subject: Re: Can printk() sleep at runtime?
To:     Steven Rostedt <rostedt@goodmis.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Stephen Boyd <sboyd@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Petr Mladek <pmladek@suse.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        SergeySenozhatsky <sergey.senozhatsky@gmail.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Michael Turquette <mturquette@baylibre.com>
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From:   Jia-Ju Bai <baijiaju1990@gmail.com>
Message-ID: <cb01782c-3947-2409-aea2-24f264f3f2ea@gmail.com>
Date:   Fri, 1 Jun 2018 08:59:39 +0800
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On 2018/6/1 5:13, Steven Rostedt wrote:
> On Thu, 31 May 2018 18:42:48 +0200
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
>> Hi Stephen,
>>
>> On Thu, May 31, 2018 at 5:19 PM, Stephen Boyd <sboyd@kernel.org> wrote:
>>> Quoting Linus Torvalds (2018-05-31 07:32:10)
>>>> On Thu, May 31, 2018 at 5:05 AM Petr Mladek <pmladek@suse.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.

Agreed.


Best wishes,
Jia-Ju Bai