Re: [PATCH v5 mm-new 0/6] mm: hugetlb: allocate frozen gigantic folio

[Zi Yan <ziy@nvidia.com>]

On 7 Jan 2026, at 13:39, Mark Brown wrote:

> On Wed, Jan 07, 2026 at 07:31:30PM +0200, Claudiu Beznea wrote:
>> On 12/30/25 09:24, Kefeng Wang wrote:
>
>>> Introduce alloc_contig_frozen_pages() and cma_alloc_frozen_compound()
>>> which avoid atomic operation about page refcount, and then convert to
>>> allocate frozen gigantic folio by the new helpers in hugetlb to cleanup
>>> the alloc_gigantic_folio().
>>
>> I'm seeing the following issues on the Renesas RZ/G3S SoC when doing suspend
>> to idle:
>>
>> [  129.636729] Unable to handle kernel paging request at virtual address
>> dead000000000108
>> [  129.644674] Mem abort info:
>> [  129.647456]   ESR = 0x0000000096000044
>
> This is also introducing OOMs when doing at least audio tests (I don't
> think these are super relevant) on Raspberry Pi 3B+ running NFS root
> (probably more relevant):
>
> [   64.064256] Unable to handle kernel paging request at virtual address fffffdffc1000000
>
> ...
>
> [   64.087583] Call trace:
> [   64.087586]  kmem_cache_free+0x88/0x434 (P)
> [   64.087598]  skb_free_head+0x9c/0xb8
> [   64.087608]  skb_release_data+0x120/0x174
> [   64.087615]  __kfree_skb+0x2c/0x44
> [   64.087622]  tcp_data_queue+0x948/0xe50
>
> Full log:
>
>   https://lava.sirena.org.uk/scheduler/job/2341856#L1721
>
> Bisection identifies:
>
> [fb9a328d30400dbc8b2ea5a57daeb28bedac398b] mm: cma: add cma_alloc_frozen{_compound}()
>
> as being the comit that introduces the issue.  Bisect log with links to
> further test runs:

Hi Mark and Claudiu,

Can you try the patch below to see if it fixes the issue? Basically,
in cma_release(), count was used to drop page ref and decreased to 0,
but after the loop, count becomes -1 and __cma_release_frozen()
is releasing unnecessary pages.

Thanks.


From ece23da65ea7210e1fcb51ee9c27aec19b84811c Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@nvidia.com>
Date: Wed, 7 Jan 2026 14:23:15 -0500
Subject: [PATCH] mm/cma: fix cma_release by not decreasing count to 0.
Content-Type: text/plain; charset="utf-8"

Signed-off-by: Zi Yan <ziy@nvidia.com>
---
 mm/cma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/cma.c b/mm/cma.c
index 5713becc602b..408b07f6fddd 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -1013,13 +1013,14 @@ bool cma_release(struct cma *cma, const struct page *pages,
 {
 	struct cma_memrange *cmr;
 	unsigned long pfn;
+	unsigned long i;

 	cmr = find_cma_memrange(cma, pages, count);
 	if (!cmr)
 		return false;

 	pfn = page_to_pfn(pages);
-	for (; count--; pfn++)
+	for (i = 0; i < count; i++, pfn++)
 		VM_WARN_ON(!put_page_testzero(pfn_to_page(pfn)));

 	__cma_release_frozen(cma, cmr, pages, count);
-- 
2.51.0




Best Regards,
Yan, Zi