linux-kernel - Re: [PATCH -next v2 2/2] blk-throttle: fix io hung due to configuration updates

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Message-ID: <20bc6370-999b-ed3c-4b8f-19b2cdba5965@huawei.com>
Date:   Thu, 19 May 2022 15:06:38 +0800
From:   "yukuai (C)" <yukuai3@...wei.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
CC:     kernel test robot <lkp@...el.com>, Tejun Heo <tj@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, Ming Lei <ming.lei@...hat.com>,
        <kbuild-all@...ts.01.org>, <cgroups@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        <yi.zhang@...wei.com>
Subject: Re: [PATCH -next v2 2/2] blk-throttle: fix io hung due to
 configuration updates



在 2022/05/19 15:01, Geert Uytterhoeven 写道:
> Hi Yukuai,
> 
> On Thu, May 19, 2022 at 5:25 AM yukuai (C) <yukuai3@...wei.com> wrote:
>> 在 2022/05/19 10:11, yukuai (C) 写道:
>>> 在 2022/05/18 23:52, kernel test robot 写道:
>>>> Thank you for the patch! Yet something to improve:
>>>>
>>>> [auto build test ERROR on next-20220517]
>>>>
>>>> url:
>>>> https://github.com/intel-lab-lkp/linux/commits/Yu-Kuai/bugfix-for-blk-throttle/20220518-151713
>>>>
>>>> base:    47c1c54d1bcd0a69a56b49473bc20f17b70e5242
>>>> config: m68k-allyesconfig
>>>> (https://download.01.org/0day-ci/archive/20220518/202205182347.tMOOqyfL-lkp@intel.com/config)
>>>>
>>>> compiler: m68k-linux-gcc (GCC) 11.3.0
>>>> reproduce (this is a W=1 build):
>>>>           wget
>>>> https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross
>>>> -O ~/bin/make.cross
>>>>           chmod +x ~/bin/make.cross
>>>>           #
>>>> https://github.com/intel-lab-lkp/linux/commit/f8345dbaf4ed491742aab29834aff66b4930c087
>>>>
>>>>           git remote add linux-review
>>>> https://github.com/intel-lab-lkp/linux
>>>>           git fetch --no-tags linux-review
>>>> Yu-Kuai/bugfix-for-blk-throttle/20220518-151713
>>>>           git checkout f8345dbaf4ed491742aab29834aff66b4930c087
>>>>           # save the config file
>>>>           mkdir build_dir && cp config build_dir/.config
>>>>           COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.3.0
>>>> make.cross W=1 O=build_dir ARCH=m68k SHELL=/bin/bash
>>>>
>>>> If you fix the issue, kindly add following tag as appropriate
>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>
>>>> All errors (new ones prefixed by >>):
>>>>
>>>>      m68k-linux-ld: block/blk-throttle.o: in function `tg_conf_updated':
>>>>>> blk-throttle.c:(.text+0x25bc): undefined reference to `__udivdi3'
>>>>>> m68k-linux-ld: blk-throttle.c:(.text+0x2626): undefined reference to
>>>>>> `__udivdi3'
>>> Hi,
>>>
>>> I'm confused here, the only place that I can relate to this:
>>>
>>>       return dispatched * new_limit / old_limit;
>>>
>>> However, I don't understand yet why this is problematic...
>>>>      `.exit.text' referenced in section `.data' of
>>>> sound/soc/codecs/tlv320adc3xxx.o: defined in discarded section
>>>> `.exit.text' of sound/soc/codecs/tlv320adc3xxx.o
>>
>> + static u64 throtl_update_bytes_disp(u64 dispatched, u64 new_limit,
>> +                                    u64 old_limit)
>> + {
>> +        if (new_limit == old_limit)
>> +                return dispatched;
>> +
>> +        if (new_limit == U64_MAX)
>> +                return 0;
>> +
>> +        return dispatched * new_limit / old_limit;
>>
>> I understand it now. I'm doing (u64 / u64), I should use div64_u64
> 
> Better, use mul_u64_u64_div_u64(), as "dispatched * new_limit"
> may overflow?
Hi,

It's right that it  can overflow, I'll handle such case in next version.
> 
>> + }
>> +
>> + static u32 throtl_update_io_disp(u32 dispatched, u32 new_limit, u32 old_limit)
>> + {
>> +        if (new_limit == old_limit)
>> +                return dispatched;
>> +
>> +        if (new_limit == UINT_MAX)
>> +                return 0;
>> +
>> +        return dispatched * new_limit / old_limit;
> 
> This is the same as above, but now operating on u32s instead of u64s.
> Likewise, can the multiplication overflow?
same as above.

Thanks,
Kuai
> 
>> + }
> 
> 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
> .
>