mm: copy_pte_range() use pte_offset_map_rw_nolock()

In copy_pte_range(), we may modify the src_pte entry after holding the
src_ptl, so convert it to using pte_offset_map_rw_nolock().  Since we
already hold the exclusive mmap_lock, and the copy_pte_range() and
retract_page_tables() are using vma->anon_vma to be exclusive, so the PTE
page is stable, there is no need to get pmdval and do pmd_same() check.

Link: https://lkml.kernel.org/r/9166f6fad806efbca72e318ab6f0f8af458056a9.1727332572.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/memory.c b/mm/memory.c
index ce5cd8d4c4011a42574cf6e05c0de5cf6e11874b..6bda739a60e8b31eb64bdccc37891a8209cd2e44 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1084,6 +1084,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
        struct mm_struct *src_mm = src_vma->vm_mm;
        pte_t *orig_src_pte, *orig_dst_pte;
        pte_t *src_pte, *dst_pte;
+       pmd_t dummy_pmdval;
        pte_t ptent;
        spinlock_t *src_ptl, *dst_ptl;
        int progress, max_nr, ret = 0;
@@ -1109,7 +1110,15 @@ again:
                ret = -ENOMEM;
                goto out;
        }
-       src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl);
+
+       /*
+        * We already hold the exclusive mmap_lock, the copy_pte_range() and
+        * retract_page_tables() are using vma->anon_vma to be exclusive, so
+        * the PTE page is stable, and there is no need to get pmdval and do
+        * pmd_same() check.
+        */
+       src_pte = pte_offset_map_rw_nolock(src_mm, src_pmd, addr, &dummy_pmdval,
+                                          &src_ptl);
        if (!src_pte) {
                pte_unmap_unlock(dst_pte, dst_ptl);
                /* ret == 0 */