[PATCH v3] mm/cma: move put_page_testzero() out of VM_WARN_ON in cma_release()

[PATCH v3] 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. Collect all !put_page_testzero()
results and check the sum using WARN instead after the loop. It restores
the same check in free_contig_range() before commit
e0c1326779cc ("mm: page_alloc: add alloc_contig_frozen_{range,pages}()"),
the commit prior to the Fixes one.

Fixes: 9bda131c6093 ("mm: cma: add cma_alloc_frozen{_compound}()")
Reported-by: Ron Economos <re@w6rz.net>
Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
Suggested-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
From V2:
- Collect !put_page_testzero() to get the right result.

From V1:
- Collect all put_page_testzero() results and do a single WARN after the
  loop.

 mm/cma.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index 94b5da468a7d..15cc0ae76c8e 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -1013,6 +1013,7 @@ bool cma_release(struct cma *cma, const struct page *pages,
 		 unsigned long count)
 {
 	struct cma_memrange *cmr;
+	unsigned long ret = 0;
 	unsigned long i, pfn;
 
 	cmr = find_cma_memrange(cma, pages, count);
@@ -1021,7 +1022,9 @@ bool cma_release(struct cma *cma, const struct page *pages,
 
 	pfn = page_to_pfn(pages);
 	for (i = 0; i < count; i++, pfn++)
-		VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)));
+		ret += !put_page_testzero(pfn_to_page(pfn));
+
+	WARN(ret, "%lu pages are still in use!\n", ret);
 
 	__cma_release_frozen(cma, cmr, pages, count);
 
-- 
2.51.0