[PATCH v2 2/5] mm: Clear vmf->pte after pte_unmap_same() returns

Peter Xu
2021-09-02T20:17:32Z

pte_unmap_same() will always unmap the pte pointer. After the unmap, vmf->pte
will not be valid any more, we should clear it.

It was safe only because no one is accessing vmf->pte after pte_unmap_same()
returns, since the only caller of pte_unmap_same() (so far) is do_swap_page(),
where vmf->pte will in most cases be overwritten very soon.

Directly pass in vmf into pte_unmap_same() and then we can also avoid the long
parameter list too, which should be a nice cleanup.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/memory.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 25fc46e87214..7b095f07c4ef 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2724,19 +2724,19 @@ EXPORT_SYMBOL_GPL(apply_to_existing_page_range);
* proceeding (but do_wp_page is only called after already making such a check;
* and do_anonymous_page can safely check later on).
*/
-static inline int pte_unmap_same(struct mm_struct *mm, pmd_t *pmd,
- pte_t *page_table, pte_t orig_pte)
+static inline int pte_unmap_same(struct vm_fault *vmf)
{
int same = 1;
#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPTION)
if (sizeof(pte_t) > sizeof(unsigned long)) {
- spinlock_t *ptl = pte_lockptr(mm, pmd);
+ spinlock_t *ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
spin_lock(ptl);
- same = pte_same(*page_table, orig_pte);
+ same = pte_same(*vmf->pte, vmf->orig_pte);
spin_unlock(ptl);
}
#endif
- pte_unmap(page_table);
+ pte_unmap(vmf->pte);
+ vmf->pte = NULL;
return same;
}

@@ -3487,7 +3487,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
vm_fault_t ret = 0;
void *shadow = NULL;

- if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
+ if (!pte_unmap_same(vmf))
goto out;

entry = pte_to_swp_entry(vmf->orig_pte);
--
2.31.1