linux-kernel - Re: [PATCH 02/13] PCI/P2PDMA: Fix the warning condition in p2pmem_alloc

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Message-ID: <4a91cfe7-75f5-49a4-89a4-fd6717e7e9d2@deltatee.com>
Date: Mon, 22 Dec 2025 09:50:18 -0700
From: Logan Gunthorpe <logang@...tatee.com>
To: Hou Tao <houtao@...weicloud.com>, linux-kernel@...r.kernel.org
Cc: linux-pci@...r.kernel.org, linux-mm@...ck.org,
 linux-nvme@...ts.infradead.org, Bjorn Helgaas <bhelgaas@...gle.com>,
 Alistair Popple <apopple@...dia.com>, Leon Romanovsky <leonro@...dia.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Tejun Heo <tj@...nel.org>,
 "Rafael J . Wysocki" <rafael@...nel.org>, Danilo Krummrich
 <dakr@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...nel.org>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Keith Busch
 <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
 Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
 houtao1@...wei.com
Subject: Re: [PATCH 02/13] PCI/P2PDMA: Fix the warning condition in
 p2pmem_alloc_mmap()

On 2025-12-19 21:04, Hou Tao wrote:
> From: Hou Tao <houtao1@...wei.com>
> 
> Commit b7e282378773 has already changed the initial page refcount of
> p2pdma page from one to zero, however, in p2pmem_alloc_mmap() it uses
> "VM_WARN_ON_ONCE_PAGE(!page_ref_count(page))" to assert the initial page
> refcount should not be zero and the following will be reported when
> CONFIG_DEBUG_VM is enabled:
> 
>  page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x380400000
>  flags: 0x20000000002000(reserved|node=0|zone=4)
>  raw: 0020000000002000 ff1100015e3ab440 0000000000000000 0000000000000000
>  raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
>  page dumped because: VM_WARN_ON_ONCE_PAGE(!page_ref_count(page))
>  ------------[ cut here ]------------
>  WARNING: CPU: 5 PID: 449 at drivers/pci/p2pdma.c:240 p2pmem_alloc_mmap+0x83a/0xa60
> 
> Fix by using "page_ref_count(page)" as the assertion condition.
> 
> Fixes: b7e282378773 ("mm/mm_init: move p2pdma page refcount initialisation to p2pdma")
> Signed-off-by: Hou Tao <houtao1@...wei.com>

Thanks for the fix

Reviewed-by: Logan Gunthorpe <logang@...tatee.com>

Logan