page_ref_freeze and page_ref_unfreeze are designed to be used as a pair.
They protect critical sections where struct page can be modified.
page_ref_unfreeze() is protected by _release() atomic operation, but
page_ref_freeze() is not as it is assumed that cmpxch provides the full
barrier.
Instead, use the appropriate atomic_cmpxchg_acquire() to ensure that
memory model is excplicitly followed.
Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
---
include/linux/page_ref.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/page_ref.h b/include/linux/page_ref.h
index 9efabeff4e06..45be731d8919 100644
--- a/include/linux/page_ref.h
+++ b/include/linux/page_ref.h
@@ -308,7 +308,8 @@ static inline bool folio_try_get_rcu(struct folio *folio)
static inline int page_ref_freeze(struct page *page, int count)
{
- int ret = likely(atomic_cmpxchg(&page->_refcount, count, 0) == count);
+ int old_val = atomic_cmpxchg_acquire(&page->_refcount, count, 0);
+ int ret = likely(old_val == count);
if (page_ref_tracepoint_active(page_ref_freeze))
__page_ref_freeze(page, count, ret);
--
2.34.1.307.g9b7440fafd-goog
