From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Subject: hugetlbfs: revert "Use i_mmap_rwsem to fix page fault/truncate race" This reverts c86aa7bbfd5568ba8a82d3635d8f7b8a8e06fe54 The reverted commit caused ABBA deadlocks when file migration raced with file eviction for specific hugetlbfs files. This was discovered with a modified version of the LTP move_pages12 test. The purpose of the reverted patch was to close a long existing race between hugetlbfs file truncation and page faults. After more analysis of the patch and impacted code, it was determined that i_mmap_rwsem can not be used for all required synchronization. Therefore, revert this patch while working an another approach to the underlying issue. Link: http://lkml.kernel.org/r/20190103235452.29335-1-mike.kravetz@xxxxxxxxxx Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Reported-by: Jan Stancek <jstancek@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Cc: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/hugetlbfs/inode.c | 61 ++++++++++++++++++++++------------------- mm/hugetlb.c | 21 +++++++------- 2 files changed, 44 insertions(+), 38 deletions(-) --- a/fs/hugetlbfs/inode.c~hugetlbfs-revert-use-i_mmap_rwsem-to-fix-page-fault-truncate-race +++ a/fs/hugetlbfs/inode.c @@ -383,16 +383,17 @@ hugetlb_vmdelete_list(struct rb_root_cac * truncation is indicated by end of range being LLONG_MAX * In this case, we first scan the range and release found pages. * After releasing pages, hugetlb_unreserve_pages cleans up region/reserv - * maps and global counts. + * maps and global counts. Page faults can not race with truncation + * in this routine. hugetlb_no_page() prevents page faults in the + * truncated range. It checks i_size before allocation, and again after + * with the page table lock for the page held. The same lock must be + * acquired to unmap a page. * hole punch is indicated if end is not LLONG_MAX * In the hole punch case we scan the range and release found pages. * Only when releasing a page is the associated region/reserv map * deleted. The region/reserv map for ranges without associated - * pages are not modified. - * - * Callers of this routine must hold the i_mmap_rwsem in write mode to prevent - * races with page faults. - * + * pages are not modified. Page faults can race with hole punch. + * This is indicated if we find a mapped page. * Note: If the passed end of range value is beyond the end of file, but * not LLONG_MAX this routine still performs a hole punch operation. */ @@ -422,14 +423,32 @@ static void remove_inode_hugepages(struc for (i = 0; i < pagevec_count(&pvec); ++i) { struct page *page = pvec.pages[i]; + u32 hash; index = page->index; + hash = hugetlb_fault_mutex_hash(h, current->mm, + &pseudo_vma, + mapping, index, 0); + mutex_lock(&hugetlb_fault_mutex_table[hash]); + /* - * A mapped page is impossible as callers should unmap - * all references before calling. And, i_mmap_rwsem - * prevents the creation of additional mappings. + * If page is mapped, it was faulted in after being + * unmapped in caller. Unmap (again) now after taking + * the fault mutex. The mutex will prevent faults + * until we finish removing the page. + * + * This race can only happen in the hole punch case. + * Getting here in a truncate operation is a bug. */ - VM_BUG_ON(page_mapped(page)); + if (unlikely(page_mapped(page))) { + BUG_ON(truncate_op); + + i_mmap_lock_write(mapping); + hugetlb_vmdelete_list(&mapping->i_mmap, + index * pages_per_huge_page(h), + (index + 1) * pages_per_huge_page(h)); + i_mmap_unlock_write(mapping); + } lock_page(page); /* @@ -451,6 +470,7 @@ static void remove_inode_hugepages(struc } unlock_page(page); + mutex_unlock(&hugetlb_fault_mutex_table[hash]); } huge_pagevec_release(&pvec); cond_resched(); @@ -462,20 +482,9 @@ static void remove_inode_hugepages(struc static void hugetlbfs_evict_inode(struct inode *inode) { - struct address_space *mapping = inode->i_mapping; struct resv_map *resv_map; - /* - * The vfs layer guarantees that there are no other users of this - * inode. Therefore, it would be safe to call remove_inode_hugepages - * without holding i_mmap_rwsem. We acquire and hold here to be - * consistent with other callers. Since there will be no contention - * on the semaphore, overhead is negligible. - */ - i_mmap_lock_write(mapping); remove_inode_hugepages(inode, 0, LLONG_MAX); - i_mmap_unlock_write(mapping); - resv_map = (struct resv_map *)inode->i_mapping->private_data; /* root inode doesn't have the resv_map, so we should check it */ if (resv_map) @@ -496,8 +505,8 @@ static int hugetlb_vmtruncate(struct ino i_mmap_lock_write(mapping); if (!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)) hugetlb_vmdelete_list(&mapping->i_mmap, pgoff, 0); - remove_inode_hugepages(inode, offset, LLONG_MAX); i_mmap_unlock_write(mapping); + remove_inode_hugepages(inode, offset, LLONG_MAX); return 0; } @@ -531,8 +540,8 @@ static long hugetlbfs_punch_hole(struct hugetlb_vmdelete_list(&mapping->i_mmap, hole_start >> PAGE_SHIFT, hole_end >> PAGE_SHIFT); - remove_inode_hugepages(inode, hole_start, hole_end); i_mmap_unlock_write(mapping); + remove_inode_hugepages(inode, hole_start, hole_end); inode_unlock(inode); } @@ -615,11 +624,7 @@ static long hugetlbfs_fallocate(struct f /* addr is the offset within the file (zero based) */ addr = index * hpage_size; - /* - * fault mutex taken here, protects against fault path - * and hole punch. inode_lock previously taken protects - * against truncation. - */ + /* mutex taken here, fault path and hole punch */ hash = hugetlb_fault_mutex_hash(h, mm, &pseudo_vma, mapping, index, addr); mutex_lock(&hugetlb_fault_mutex_table[hash]); --- a/mm/hugetlb.c~hugetlbfs-revert-use-i_mmap_rwsem-to-fix-page-fault-truncate-race +++ a/mm/hugetlb.c @@ -3755,16 +3755,16 @@ static vm_fault_t hugetlb_no_page(struct } /* - * We can not race with truncation due to holding i_mmap_rwsem. - * Check once here for faults beyond end of file. + * Use page lock to guard against racing truncation + * before we get page_table_lock. */ - size = i_size_read(mapping->host) >> huge_page_shift(h); - if (idx >= size) - goto out; - retry: page = find_lock_page(mapping, idx); if (!page) { + size = i_size_read(mapping->host) >> huge_page_shift(h); + if (idx >= size) + goto out; + /* * Check for page in userfault range */ @@ -3854,6 +3854,9 @@ retry: } ptl = huge_pte_lock(h, mm, ptep); + size = i_size_read(mapping->host) >> huge_page_shift(h); + if (idx >= size) + goto backout; ret = 0; if (!huge_pte_none(huge_ptep_get(ptep))) @@ -3956,10 +3959,8 @@ vm_fault_t hugetlb_fault(struct mm_struc /* * Acquire i_mmap_rwsem before calling huge_pte_alloc and hold - * until finished with ptep. This serves two purposes: - * 1) It prevents huge_pmd_unshare from being called elsewhere - * and making the ptep no longer valid. - * 2) It synchronizes us with file truncation. + * until finished with ptep. This prevents huge_pmd_unshare from + * being called elsewhere and making the ptep no longer valid. * * ptep could have already be assigned via huge_pte_offset. That * is OK, as huge_pte_alloc will return the same value unless _
