linux-kernel - Re: [PATCH v3 0/2] hugetlbfs: use i_mmap

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Date:   Mon, 24 Dec 2018 13:13:49 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
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>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 0/2] hugetlbfs: use i_mmap_rwsem for better
 synchronization

On Sat, Dec 22, 2018 at 02:30:11PM -0800, Mike Kravetz wrote:
> There are two primary issues addressed here:
> 1) For shared pmds, huge PTE 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.
> 
> v2 -> v3
>   Incorporated suggestions from Kirill.  Code change to hold i_mmap_rwsem
>   for duration of copy in copy_hugetlb_page_range.  Took i_mmap_rwsem in
>   hugetlbfs_evict_inode to be consistent with other callers.  Other changes
>   were to documentation/comments.
> v1 -> v2
>   Combined patches 2 and 3 of v1 series as suggested by Aneesh.  No other
>   changes were made.
> 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.
> 
> Mike Kravetz (2):
>   hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization
>   hugetlbfs: Use i_mmap_rwsem to fix page fault/truncate race

Looks good to me.

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov