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Subject[PATCH v2 02/24] mm: Clear vmf->pte after pte_unmap_same() returns
Date
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.

pte_unmap_same() will be used in other places in follow up patches, so that
vmf->pte will not always be re-written. This patch enables us to call
functions like finish_fault() because that'll conditionally unmap the pte by
checking vmf->pte first. Or, alloc_set_pte() will make sure to allocate a new
pte even after calling pte_unmap_same().

Since we'll need to modify vmf->pte, directly pass in vmf into pte_unmap_same()
and then we can also avoid the long parameter list.

Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/memory.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index ffda19542bc6d..955a0bb6b855c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2618,19 +2618,20 @@ 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);
+ /* After unmap of pte, the pointer is invalid now - clear it. */
+ vmf->pte = NULL;
return same;
}

@@ -3319,7 +3320,7 @@ 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);
--
2.26.2
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