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SubjectRe: [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,
> 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 A. Shutemov

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