mm/mremap: retry if either pte_offset_map_*lock() fails

move_ptes() return -EAGAIN if pte_offset_map_lock() of old fails, or if
pte_offset_map_nolock() of new fails: move_page_tables() retry if so.

But that does need a pmd_none() check inside, to stop endless loop when
huge shmem is truncated (thank you to syzbot); and move_huge_pmd() must
tolerate that a page table might have been allocated there just before (of
course it would be more satisfying to remove the empty page table, but
this is not a path worth optimizing).

Link: https://lkml.kernel.org/r/65e5e84a-f04-947-23f2-b97d3462e1e@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9ccdb3f..e21b3e3 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1760,9 +1760,10 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
 
        /*
         * The destination pmd shouldn't be established, free_pgtables()
-        * should have release it.
+        * should have released it; but move_page_tables() might have already
+        * inserted a page table, if racing against shmem/file collapse.
         */
-       if (WARN_ON(!pmd_none(*new_pmd))) {
+       if (!pmd_none(*new_pmd)) {
                VM_BUG_ON(pmd_trans_huge(*new_pmd));
                return false;
        }

diff --git a/mm/mremap.c b/mm/mremap.c
index da107f2..bfc3d19 100644 (file)
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -133,7 +133,7 @@ static pte_t move_soft_dirty_pte(pte_t pte)
        return pte;
 }
 
-static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
+static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
                unsigned long old_addr, unsigned long old_end,
                struct vm_area_struct *new_vma, pmd_t *new_pmd,
                unsigned long new_addr, bool need_rmap_locks)
@@ -143,6 +143,7 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
        spinlock_t *old_ptl, *new_ptl;
        bool force_flush = false;
        unsigned long len = old_end - old_addr;
+       int err = 0;
 
        /*
         * When need_rmap_locks is true, we take the i_mmap_rwsem and anon_vma
@@ -170,8 +171,16 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
         * pte locks because exclusive mmap_lock prevents deadlock.
         */
        old_pte = pte_offset_map_lock(mm, old_pmd, old_addr, &old_ptl);
-       new_pte = pte_offset_map(new_pmd, new_addr);
-       new_ptl = pte_lockptr(mm, new_pmd);
+       if (!old_pte) {
+               err = -EAGAIN;
+               goto out;
+       }
+       new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl);
+       if (!new_pte) {
+               pte_unmap_unlock(old_pte, old_ptl);
+               err = -EAGAIN;
+               goto out;
+       }
        if (new_ptl != old_ptl)
                spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING);
        flush_tlb_batched_pending(vma->vm_mm);
@@ -208,8 +217,10 @@ static void move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd,
                spin_unlock(new_ptl);
        pte_unmap(new_pte - 1);
        pte_unmap_unlock(old_pte - 1, old_ptl);
+out:
        if (need_rmap_locks)
                drop_rmap_locks(vma);
+       return err;
 }
 
 #ifndef arch_supports_page_table_move
@@ -537,6 +548,7 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
                new_pmd = alloc_new_pmd(vma->vm_mm, vma, new_addr);
                if (!new_pmd)
                        break;
+again:
                if (is_swap_pmd(*old_pmd) || pmd_trans_huge(*old_pmd) ||
                    pmd_devmap(*old_pmd)) {
                        if (extent == HPAGE_PMD_SIZE &&
@@ -544,8 +556,6 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
                                           old_pmd, new_pmd, need_rmap_locks))
                                continue;
                        split_huge_pmd(vma, old_pmd, old_addr);
-                       if (pmd_trans_unstable(old_pmd))
-                               continue;
                } else if (IS_ENABLED(CONFIG_HAVE_MOVE_PMD) &&
                           extent == PMD_SIZE) {
                        /*
@@ -556,11 +566,13 @@ unsigned long move_page_tables(struct vm_area_struct *vma,
                                           old_pmd, new_pmd, true))
                                continue;
                }
-
+               if (pmd_none(*old_pmd))
+                       continue;
                if (pte_alloc(new_vma->vm_mm, new_pmd))
                        break;
-               move_ptes(vma, old_pmd, old_addr, old_addr + extent, new_vma,
-                         new_pmd, new_addr, need_rmap_locks);
+               if (move_ptes(vma, old_pmd, old_addr, old_addr + extent,
+                             new_vma, new_pmd, new_addr, need_rmap_locks) < 0)
+                       goto again;
        }
 
        mmu_notifier_invalidate_range_end(&range);