Commit 6dfd0d2c authored by Qi Zheng's avatar Qi Zheng Committed by Andrew Morton
Browse files

mm: khugepaged: collapse_pte_mapped_thp() use pte_offset_map_rw_nolock() 

In collapse_pte_mapped_thp(), we may modify the pte and pmd entry after
acquiring the ptl, so convert it to using pte_offset_map_rw_nolock().  At
this time, the pte_same() check is not performed after the PTL held.  So
we should get pgt_pmd and do pmd_same() check after the ptl held.

Link: https://lkml.kernel.org/r/055e42db68da00ac8ecab94bd2633c7cd965eb1c.1727332572.git.zhengqi.arch@bytedance.com


Signed-off-by: default avatarQi Zheng <zhengqi.arch@bytedance.com>
Reviewed-by: default avatarMuchun 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent d9c1ddf3

mm/khugepaged.c

+13 −5
Original line number Diff line number Diff line
@@ -1608,7 +1608,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, 
	if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))

		pml = pmd_lock(mm, pmd);



	start_pte = pte_offset_map_nolock(mm, pmd, haddr, &ptl);

	start_pte = pte_offset_map_rw_nolock(mm, pmd, haddr, &pgt_pmd, &ptl);

	if (!start_pte)		/* mmap_lock + page lock should prevent this */

		goto abort;

	if (!pml)
@@ -1616,6 +1616,9 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, 
	else if (ptl != pml)

		spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);



	if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd))))

		goto abort;



	/* step 2: clear page table and adjust rmap */

	for (i = 0, addr = haddr, pte = start_pte;

	     i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE, pte++) {
@@ -1648,7 +1651,6 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, 
		nr_ptes++;

	}



	pte_unmap(start_pte);

	if (!pml)

		spin_unlock(ptl);
@@ -1661,13 +1663,18 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, 
	/* step 4: remove empty page table */

	if (!pml) {

		pml = pmd_lock(mm, pmd);

		if (ptl != pml)

		if (ptl != pml) {

			spin_lock_nested(ptl, SINGLE_DEPTH_NESTING);

			if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) {

				flush_tlb_mm(mm);

				goto unlock;

			}

		}

	}

	pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd);

	pmdp_get_lockless_sync();

	pte_unmap_unlock(start_pte, ptl);

	if (ptl != pml)

		spin_unlock(ptl);

		spin_unlock(pml);



	mmu_notifier_invalidate_range_end(&range);
@@ -1688,6 +1695,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, 
		folio_ref_sub(folio, nr_ptes);

		add_mm_counter(mm, mm_counter_file(folio), -nr_ptes);

	}

unlock:

	if (start_pte)

		pte_unmap_unlock(start_pte, ptl);

	if (pml && pml != ptl)