Re: [PATCH 3/6] bitmap_parselist: rework input string parser

[Yuri Norov]

+ Mike Travis <travis@xxxxxxx>
+ Thomas Gleixner <tglx@xxxxxxxxxxxxx>

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On Tue, Mar 26, 2019 at 12:07:45AM +0300, Yury Norov wrote:
>> The requirement for this rework is to keep the __bitmap_parselist()
>> copy-less and single-pass but make it more readable and maintainable by
>> splitting into logical parts and removing explicit nested cycles and
>> opaque local variables.
>>
>> __bitmap_parselist() can parse userspace inputs and therefore we cannot
>> use simple_strtoul() to parse numbers.

> So, all above depends to what memory we access kernel / user space.
> Perhaps we can get copy of memory of a given size and then parse it in kernel space always?

> --
> With Best Regards,
> Andy Shevchenko

What I missed during rework is that we have only one caller of *parselist_user  -
it's write_irq_affinity() introduced by Mike Travis in kernel/irq/proc.c. It doesn't look
like a hot path as it's file operations handler. If no objections from Mike or Thomas,
I think it would make sense to copy_from_user() the userspace data at the beginning
in sake of simplicity of __bitmap_parselist(), as you suggested above.

Yury