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Wysocki" , Danilo Krummrich , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , houtao1@huawei.com References: <20251220040446.274991-1-houtao@huaweicloud.com> <20251220040446.274991-3-houtao@huaweicloud.com> Content-Language: en-CA From: Logan Gunthorpe In-Reply-To: <20251220040446.274991-3-houtao@huaweicloud.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: houtao@huaweicloud.com, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-mm@kvack.org, linux-nvme@lists.infradead.org, bhelgaas@google.com, apopple@nvidia.com, leonro@nvidia.com, gregkh@linuxfoundation.org, tj@kernel.org, rafael@kernel.org, dakr@kernel.org, akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, kbusch@kernel.org, axboe@kernel.dk, hch@lst.de, sagi@grimberg.me, houtao1@huawei.com X-SA-Exim-Mail-From: logang@deltatee.com X-Spam-Level: Subject: Re: [PATCH 02/13] PCI/P2PDMA: Fix the warning condition in p2pmem_alloc_mmap() X-SA-Exim-Version: 4.2.1 (built Sun, 23 Feb 2025 07:57:16 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) On 2025-12-19 21:04, Hou Tao wrote: > From: Hou Tao > > 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 Thanks for the fix Reviewed-by: Logan Gunthorpe Logan