linux-kernel - Re: [PATCH 0/3] hugetlbfs fallocate hole punch race with page faults

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Date:	Mon, 19 Oct 2015 16:18:40 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mike Kravetz <mike.kravetz@...cle.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH 0/3] hugetlbfs fallocate hole punch race with page
 faults

On Fri, 16 Oct 2015 15:08:27 -0700 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> The hugetlbfs fallocate hole punch code can race with page faults.  The
> result is that after a hole punch operation, pages may remain within the
> hole.  No other side effects of this race were observed.
> 
> In preparation for adding userfaultfd support to hugetlbfs, it is desirable
> to plug or significantly shrink this hole.  This patch set uses the same
> mechanism employed in shmem (see commit f00cdc6df7).
> 

"still buggy but not as bad as before" isn't what we strive for ;) What
would it take to fix this for real?  An exhaustive description of the
bug would be a good starting point, thanks.
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