diff --git a/mm/memory.c b/mm/memory.c index c8d5d040d6ab..ce5cd8d4c401 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5742,14 +5742,24 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf) vmf->pte = NULL; vmf->flags &= ~FAULT_FLAG_ORIG_PTE_VALID; } else { + pmd_t dummy_pmdval; + /* * A regular pmd is established and it can't morph into a huge * pmd by anon khugepaged, since that takes mmap_lock in write * mode; but shmem or file collapse to THP could still morph * it into a huge pmd: just retry later if so. + * + * Use the maywrite version to indicate that vmf->pte may be + * modified, but since we will use pte_same() to detect the + * change of the !pte_none() entry, there is no need to recheck + * the pmdval. Here we chooes to pass a dummy variable instead + * of NULL, which helps new user think about why this place is + * special. */ - vmf->pte = pte_offset_map_nolock(vmf->vma->vm_mm, vmf->pmd, - vmf->address, &vmf->ptl); + vmf->pte = pte_offset_map_rw_nolock(vmf->vma->vm_mm, vmf->pmd, + vmf->address, &dummy_pmdval, + &vmf->ptl); if (unlikely(!vmf->pte)) return 0; vmf->orig_pte = ptep_get_lockless(vmf->pte);