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@xxxxxxxxxx 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 fs/hugetlbfs/inode.c | 61 +++++++++++++++----------------- mm/hugetlb.c | 84 +++++++++++++++++++++++++++++++------------- mm/memory-failure.c | 14 +++++++- mm/migrate.c | 13 ++++++- mm/rmap.c | 4 +++ mm/userfaultfd.c | 11 ++++-- 6 files changed, 125 insertions(+), 62 deletions(-) -- 2.17.2
