[PATCH] mm/cma: move put_page_testzero() out of VM_WARN_ON in cma_release()

[Zi Yan]

When CONFIG_DEBUG_VM is not set, VM_WARN_ON is a NOP. Putting any statement
with side effect inside it is incorrect. Move put_page_testzero() out and
check its return value in VM_WARN_ON. Add __maybe_unused to the return
value for when CONFIG_DEBUG_VM is not set.

Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
Reported-by: Ron Economos <re@xxxxxxxx>
Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@xxxxxxxx/
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
Alternatively, we can use WARN_ON instead. Let me know.

 mm/cma.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/cma.c b/mm/cma.c
index 94b5da468a7d..a9fe6e9a9215 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -1020,8 +1020,11 @@ bool cma_release(struct cma *cma, const struct page *pages,
 		return false;
 
 	pfn = page_to_pfn(pages);
-	for (i = 0; i < count; i++, pfn++)
-		VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)));
+	for (i = 0; i < count; i++, pfn++) {
+		int __maybe_unused ret = put_page_testzero(pfn_to_page(pfn));
+
+		VM_WARN_ON(!ret);
+	}
 
 	__cma_release_frozen(cma, cmr, pages, count);
 
-- 
2.51.0