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SubjectRe: [PATCH RFC 0/3] A few round_pipe_size() and pipe-max-size fixups
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On 09/14/17 12:19, Joe Lawrence wrote:
> On 09/14/2017 12:57 PM, Randy Dunlap wrote:
>> On 09/14/17 06:26, Michael Kerrisk (man-pages) wrote:
>>> Hello Joe,
>>>
>>> On 5 September 2017 at 16:44, Joe Lawrence <joe.lawrence@redhat.com> wrote:
>>>> While backporting Michael's "pipe: fix limit handling" [1] patchset to a
>>>> distro-kernel, Mikulas noticed that current upstream pipe limit handling
>>>> contains a few problems:
>>>>
>>>> 1 - round_pipe_size() nr_pages overflow on 32bit: this would
>>>> subsequently try roundup_pow_of_two(0), which is undefined.
>>
>> Hi,
>> Sorry I missed the initial posting of this.
>>
>> The man page for F_SETPIPE_SZ (http://man7.org/linux/man-pages/man2/fcntl.2.html)
>> says:
>> "Attempts to set the pipe capacity below the page size are
>> silently rounded up to the page size."
>>
>> That implies to me that setting pipe size to 0 would round up to PAGE_SIZE.
>> Doesn't patch 1/3 change that to return -EINVAL?
>
> Good catch. How about something like this:
>
> /*
> * Minimum pipe size, as required by POSIX
> */
> unsigned int pipe_min_size = PAGE_SIZE;
>
> ...
>
> static inline unsigned int round_pipe_size(unsigned int size)
> {
> unsigned long nr_pages;
>
> + if (size < pipe_min_size)
> + size = pipe_min_size;
> +
> nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> if (nr_pages == 0)
> return 0;
>
>>
>> Otherwise all 3 patches look good to me.
>
> If the above is good, I can fold this into patch 1 and respin the set.

Yes, looks good to me. Thanks.


--
~Randy

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