linux-kernel - Re: [PATCH 0/3] hugetlbfs: use i_mmap

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Message-Id: <20181214132239.9b74e2ca4bc4e38a409736dc@linux-foundation.org>
Date:   Fri, 14 Dec 2018 13:22:39 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Prakash Sangappa <prakash.sangappa@...cle.com>
Subject: Re: [PATCH 0/3] hugetlbfs: use i_mmap_rwsem for better
 synchronization

On Mon,  3 Dec 2018 12:08:47 -0800 Mike Kravetz <mike.kravetz@...cle.com> wrote:

> These patches are a follow up to the RFC,
> http://lkml.kernel.org/r/20181024045053.1467-1-mike.kravetz@oracle.com
> Comments made by Naoya were addressed.
> 
> There are two primary issues addressed here:
> 1) For shared pmds, huge PE pointers returned by huge_pte_alloc can become
>    invalid via a call to huge_pmd_unshare by another thread.
> 2) hugetlbfs page faults can race with truncation causing invalid global
>    reserve counts and state.
> Both issues are addressed by expanding the use of i_mmap_rwsem.
> 
> These issues have existed for a long time.  They can be recreated with a
> test program that causes page fault/truncation races.  For simple mappings,
> this results in a negative HugePages_Rsvd count.  If racing with mappings
> that contain shared pmds, we can hit "BUG at fs/hugetlbfs/inode.c:444!" or
> Oops! as the result of an invalid memory reference.
> 
> I broke up the larger RFC into separate patches addressing each issue.
> Hopefully, this is easier to understand/review.

Three patches tagged for -stable and no reviewers yet.  Could people
please take a close look?