linux-kernel - [PATCH 0/3] hugetlbfs: use i_mmap_rwsem for better synchronization

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Message-Id: <20181203200850.6460-1-mike.kravetz@oracle.com>
Date:   Mon,  3 Dec 2018 12:08:47 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     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>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 0/3] hugetlbfs: use i_mmap_rwsem for better synchronization

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.

Mike Kravetz (3):
  hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization
  hugetlbfs: Use i_mmap_rwsem to fix page fault/truncate race
  hugetlbfs: remove unnecessary code after i_mmap_rwsem synchronization

 fs/hugetlbfs/inode.c | 50 +++++++++----------------
 mm/hugetlb.c         | 87 +++++++++++++++++++++++++++++++-------------
 mm/memory-failure.c  | 14 ++++++-
 mm/migrate.c         | 13 ++++++-
 mm/rmap.c            |  3 ++
 mm/userfaultfd.c     | 11 +++++-
 6 files changed, 116 insertions(+), 62 deletions(-)

-- 
2.17.2