In handle_pte_fault(), we may modify the vmf->pte after acquiring the
vmf->ptl, so convert it to using pte_offset_map_rw_nolock(). But since we
will do the pte_same() check, so there is no need to get pmdval to do
pmd_same() check, just pass a dummy variable to it.
Signed-off-by: Qi Zheng <zhengqi.a...@bytedance.com>
Acked-by: David Hildenbrand <da...@redhat.com>
Reviewed-by: Muchun Song <muchun.s...@linux.dev>
---
mm/memory.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 42674c0748cba..06674f94b7a4e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5498,14 +5498,24 @@ 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);
--
2.20.1
