diff options
author | Mike Kravetz <mike.kravetz@oracle.com> | 2022-09-14 15:18:03 -0700 |
---|---|---|
committer | Andrew Morton <akpm@linux-foundation.org> | 2022-10-03 14:03:16 -0700 |
commit | 3a47c54f09c4c89128d8f67d49296b1c25b317d0 (patch) | |
tree | 51a6ef70b2d991bd8c051c9fb8f85904961e9661 /mm/rmap.c | |
parent | 188a39725ad7ded2d13e752a1a620152b0750175 (diff) | |
download | linux-3a47c54f09c4c89128d8f67d49296b1c25b317d0.tar.gz |
hugetlbfs: revert use i_mmap_rwsem for more pmd sharing synchronization
Commit c0d0381ade79 ("hugetlbfs: use i_mmap_rwsem for more pmd sharing synchronization") added code to take i_mmap_rwsem in read mode for the duration of fault processing. However, this has been shown to cause performance/scaling issues. Revert the code and go back to only taking the semaphore in huge_pmd_share during the fault path. Keep the code that takes i_mmap_rwsem in write mode before calling try_to_unmap as this is required if huge_pmd_unshare is called. NOTE: Reverting this code does expose the following race condition. Faulting thread Unsharing thread ... ... ptep = huge_pte_offset() or ptep = huge_pte_alloc() ... i_mmap_lock_write lock page table ptep invalid <------------------------ huge_pmd_unshare() Could be in a previously unlock_page_table sharing process or worse i_mmap_unlock_write ... ptl = huge_pte_lock(ptep) get/update pte set_pte_at(pte, ptep) It is unknown if the above race was ever experienced by a user. It was discovered via code inspection when initially addressed. In subsequent patches, a new synchronization mechanism will be added to coordinate pmd sharing and eliminate this race. Link: https://lkml.kernel.org/r/20220914221810.95771-3-mike.kravetz@oracle.com Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> Reviewed-by: Miaohe Lin <linmiaohe@huawei.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Axel Rasmussen <axelrasmussen@google.com> Cc: David Hildenbrand <david@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: James Houghton <jthoughton@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Mina Almasry <almasrymina@google.com> Cc: Muchun Song <songmuchun@bytedance.com> Cc: Naoya Horiguchi <naoya.horiguchi@linux.dev> Cc: Pasha Tatashin <pasha.tatashin@soleen.com> Cc: Peter Xu <peterx@redhat.com> Cc: Prakash Sangappa <prakash.sangappa@oracle.com> Cc: Sven Schnelle <svens@linux.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
-rw-r--r-- | mm/rmap.c | 8 |
1 files changed, 1 insertions, 7 deletions
diff --git a/mm/rmap.c b/mm/rmap.c index 0b9264e58d25..2a08647a61fc 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -23,10 +23,9 @@ * inode->i_rwsem (while writing or truncating, not reading or faulting) * mm->mmap_lock * mapping->invalidate_lock (in filemap_fault) - * page->flags PG_locked (lock_page) * (see hugetlbfs below) + * page->flags PG_locked (lock_page) * hugetlbfs_i_mmap_rwsem_key (in huge_pmd_share) * mapping->i_mmap_rwsem - * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) * anon_vma->rwsem * mm->page_table_lock or pte_lock * swap_lock (in swap_duplicate, swap_info_get) @@ -45,11 +44,6 @@ * anon_vma->rwsem,mapping->i_mmap_rwsem (memory_failure, collect_procs_anon) * ->tasklist_lock * pte map lock - * - * * hugetlbfs PageHuge() pages take locks in this order: - * mapping->i_mmap_rwsem - * hugetlb_fault_mutex (hugetlbfs specific page fault mutex) - * page->flags PG_locked (lock_page) */ #include <linux/mm.h> |