From 838d02354464c301fcddf4f524365846608ac296 Mon Sep 17 00:00:00 2001 From: Qi Zheng Date: Thu, 26 Sep 2024 14:46:22 +0800 Subject: [PATCH] mm: mremap: move_ptes() use pte_offset_map_rw_nolock() In move_ptes(), we may modify the new_pte after acquiring the new_ptl, so convert it to using pte_offset_map_rw_nolock(). Now new_pte is none, so hpage_collapse_scan_file() path can not find this by traversing file->f_mapping, so there is no concurrency with retract_page_tables(). In addition, we already hold the exclusive mmap_lock, so this new_pte page is stable, so there is no need to get pmdval and do pmd_same() check. Link: https://lkml.kernel.org/r/9d582a09dbcf12e562ac5fe0ba05e9248a58f5e0.1727332572.git.zhengqi.arch@bytedance.com Signed-off-by: Qi Zheng Reviewed-by: Muchun Song Cc: David Hildenbrand Cc: Hugh Dickins Cc: Matthew Wilcox Cc: Mike Rapoport (Microsoft) Cc: Peter Xu Cc: Ryan Roberts Cc: Vishal Moola (Oracle) Signed-off-by: Andrew Morton --- mm/mremap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/mremap.c b/mm/mremap.c index dda09e957a5d4..5917feafe8cc5 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -140,6 +140,7 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, { struct mm_struct *mm = vma->vm_mm; pte_t *old_pte, *new_pte, pte; + pmd_t dummy_pmdval; spinlock_t *old_ptl, *new_ptl; bool force_flush = false; unsigned long len = old_end - old_addr; @@ -175,7 +176,15 @@ static int move_ptes(struct vm_area_struct *vma, pmd_t *old_pmd, err = -EAGAIN; goto out; } - new_pte = pte_offset_map_nolock(mm, new_pmd, new_addr, &new_ptl); + /* + * Now new_pte is none, so hpage_collapse_scan_file() path can not find + * this by traversing file->f_mapping, so there is no concurrency with + * retract_page_tables(). In addition, we already hold the exclusive + * mmap_lock, so this new_pte page is stable, so there is no need to get + * pmdval and do pmd_same() check. + */ + new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &dummy_pmdval, + &new_ptl); if (!new_pte) { pte_unmap_unlock(old_pte, old_ptl); err = -EAGAIN; -- 2.49.0