[v1] mm/cma: move put_page_testzero() out of VM_WARN_ON in cma_release()

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

Posted by Zi Yan 1 month, 3 weeks ago

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@w6rz.net>
Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
Signed-off-by: Zi Yan <ziy@nvidia.com>
---
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

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

Posted by SeongJae Park 1 month, 2 weeks ago

On Tue, 24 Feb 2026 16:39:46 -0500 Zi Yan <ziy@nvidia.com> wrote:

> 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@w6rz.net>
> Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
> Signed-off-by: Zi Yan <ziy@nvidia.com>

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

[...]

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

Posted by SeongJae Park 1 month, 2 weeks ago

On Tue, 24 Feb 2026 18:18:44 -0800 SeongJae Park <sj@kernel.org> wrote:

> On Tue, 24 Feb 2026 16:39:46 -0500 Zi Yan <ziy@nvidia.com> wrote:
> 
> > 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@w6rz.net>
> > Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/

I forgot asking this, sorry.

Should we Cc stable@ ?


Thanks,
SJ

[...]

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

Posted by Zi Yan 1 month, 2 weeks ago

On 24 Feb 2026, at 21:20, SeongJae Park wrote:

> On Tue, 24 Feb 2026 18:18:44 -0800 SeongJae Park <sj@kernel.org> wrote:
>
>> On Tue, 24 Feb 2026 16:39:46 -0500 Zi Yan <ziy@nvidia.com> wrote:
>>
>>> 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@w6rz.net>
>>> Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
>
> I forgot asking this, sorry.
>
> Should we Cc stable@ ?

The commit is just in 7.0-rc1. Nothing is needed for stable.

Best Regards,
Yan, Zi

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

Posted by SeongJae Park 1 month, 2 weeks ago

On Tue, 24 Feb 2026 21:21:55 -0500 Zi Yan <ziy@nvidia.com> wrote:

> On 24 Feb 2026, at 21:20, SeongJae Park wrote:
> 
> > On Tue, 24 Feb 2026 18:18:44 -0800 SeongJae Park <sj@kernel.org> wrote:
> >
> >> On Tue, 24 Feb 2026 16:39:46 -0500 Zi Yan <ziy@nvidia.com> wrote:
> >>
> >>> 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@w6rz.net>
> >>> Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
> >
> > I forgot asking this, sorry.
> >
> > Should we Cc stable@ ?
> 
> The commit is just in 7.0-rc1. Nothing is needed for stable.

Ack.


Thanks,
SJ

[...]

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

Posted by Zi Yan 1 month, 2 weeks ago

On 24 Feb 2026, at 16:39, Zi Yan wrote:

> 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@w6rz.net>
> Closes: https://lore.kernel.org/all/1b17c38f-30d3-4bb4-a7e1-e74b19ada885@w6rz.net/
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---
> Alternatively, we can use WARN_ON instead. Let me know.
>
>  mm/cma.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>

Kefeng suggested a better solution[1]. Will update this one soon.

[1] https://lore.kernel.org/all/4b219cd0-9391-4edb-83c0-b6a1c60d0790@huawei.com

Best Regards,
Yan, Zi