[PATCH RFC 09/10] mm/hugetlb: Make hugetlb_fault() RCU-safe

Peter Xu
2022-10-30T21:30:49Z

RCU makes sure the pte_t* won't go away from under us. Please refer to the
comment above huge_pte_offset() for more information.

Signed-off-by: Peter Xu <peterx@redhat.com>
---
mm/hugetlb.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5dc87e4e6780..6d336d286394 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5822,6 +5822,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
int need_wait_lock = 0;
unsigned long haddr = address & huge_page_mask(h);

+ /* For huge_pte_offset() */
+ rcu_read_lock();
ptep = huge_pte_offset(mm, haddr, huge_page_size(h));
if (ptep) {
/*
@@ -5830,13 +5832,15 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
* not actually modifying content here.
*/
entry = huge_ptep_get(ptep);
+ rcu_read_unlock();
if (unlikely(is_hugetlb_entry_migration(entry))) {
migration_entry_wait_huge(vma, ptep);
return 0;
} else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
return VM_FAULT_HWPOISON_LARGE |
VM_FAULT_SET_HINDEX(hstate_index(h));
- }
+ } else
+ rcu_read_unlock();

/*
* Serialize hugepage allocation and instantiation, so that we don't
--
2.37.3