linux-kernel - Re: [patch][resend] MAP_HUGETLB munmap fails with size not 2MB aligned

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Date:	Mon, 30 Mar 2015 12:03:21 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Eric B Munson <emunson@...mai.com>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	David Rientjes <rientjes@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Joern Engel <joern@...fs.org>,
	Jianguo Wu <wujianguo@...wei.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [patch][resend] MAP_HUGETLB munmap fails with size not 2MB aligned

On Thu, Mar 26, 2015 at 10:08 AM, Eric B Munson <emunson@...mai.com> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On 03/26/2015 07:56 AM, Davide Libenzi wrote:
>> On Wed, 25 Mar 2015, David Rientjes wrote:
>>
>>> I looked at this thread at http://marc.info/?t=141392508800001
>>> since I didn't have it in my mailbox, and I didn't get a chance
>>> to actually run your test code.
>>>
>>> In short, I think what you're saying is that
>>>
>>> ptr = mmap(..., 4KB, ..., MAP_HUGETLB | ..., ...) munmap(ptr,
>>> 4KB) == EINVAL
>>
>> I am not sure you have read the email correctly:
>>
>> munmap(mmap(size, HUGETLB), size) = EFAIL
>>
>> For every size not multiple of the huge page size. Whereas:
>>
>> munmap(mmap(size, HUGETLB), ALIGN(size, HUGEPAGE_SIZE)) = OK
>
> I think Davide is right here, this is a long existing bug in the
> MAP_HUGETLB implementation.  Specifically, the mmap man page says:
>
> All pages containing a part of the indicated range are unmapped, and
> subsequent references to these pages will generate SIGSEGV.
>
> I realize that huge pages may not have been considered by those that
> wrote the spec.  But if I read this I would assume that all pages,
> regardless of size, touched by the munmap() request should be unmapped.
>
> Please include
> Acked-by: Eric B Munson <emunson@...mai.com>
> to the original patch.  I would like to see the mmap man page adjusted
> to make note of this behavior as well.

This is just a bug fix and I never think this has large risk. But
caution, we might revert immediately
if this patch arise some regression even if it's come from broken
application code.

Acked-by: KOSAKI Motohiro <kosaki.motohiro@...il.com>
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