[PATCH RFC 04/10] mm/hugetlb: Make userfaultfd_huge_must_wait() RCU-safe

Peter Xu
2022-10-30T21:30:59Z

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>
---
fs/userfaultfd.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 07c81ab3fd4d..4e813e68e4f8 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -243,6 +243,9 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,

mmap_assert_locked(mm);

+ /* For huge_pte_offset() */
+ rcu_read_lock();
+
ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma));

if (!ptep)
@@ -261,6 +264,7 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
ret = true;
out:
+ rcu_read_unlock();
return ret;
}
#else
--
2.37.3