On 2024/9/4 16:40, Qi Zheng wrote:
In move_ptes(), we may modify the new_pte after acquiring the new_ptl, so convert it to using pte_offset_map_rw_nolock(). Since we may free the PTE page in retract_page_tables() without holding the read lock of mmap_lock, so we still need to do a pmd_same() check after holding the PTL.
retract_page_tables() and move_ptes() are synchronized with i_mmap_lock, right? Muchun, Thanks.
Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com> --- mm/mremap.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/mm/mremap.c b/mm/mremap.c index 24712f8dbb6b5..16e54151395ad 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -143,6 +143,7 @@ static int 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; + pmd_t pmdval; int err = 0;/*@@ -175,14 +176,29 @@ 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); + /* + * Since we may free the PTE page in retract_page_tables() without + * holding the read lock of mmap_lock, so we still need to do a + * pmd_same() check after holding the PTL. + */ + new_pte = pte_offset_map_rw_nolock(mm, new_pmd, new_addr, &pmdval, + &new_ptl); if (!new_pte) { pte_unmap_unlock(old_pte, old_ptl); err = -EAGAIN; goto out; } - if (new_ptl != old_ptl) + if (new_ptl != old_ptl) { spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); + + if (unlikely(!pmd_same(pmdval, pmdp_get_lockless(new_pmd)))) { + pte_unmap_unlock(new_pte, new_ptl); + pte_unmap_unlock(old_pte, old_ptl); + err = -EAGAIN; + goto out; + } + } + flush_tlb_batched_pending(vma->vm_mm); arch_enter_lazy_mmu_mode();
