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Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.98.2) (envelope-from ) id 1vfnvG-00000000mAR-2Lj7; Tue, 13 Jan 2026 16:35:39 -0700 Message-ID: Date: Tue, 13 Jan 2026 16:34:59 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Alistair Popple , helgaas@kernel.org Cc: 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, 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 References: <20260112005440.998543-1-apopple@nvidia.com> Content-Language: en-CA From: Logan Gunthorpe In-Reply-To: <20260112005440.998543-1-apopple@nvidia.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: apopple@nvidia.com, helgaas@kernel.org, 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, 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 Subject: Re: [PATCH] PCI/P2PDMA: Reset page reference count when page mapping fails 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) X-Rspam-User: X-Stat-Signature: b1osybhh3i15gmjq379aen117tf17asq X-Rspamd-Queue-Id: C2B37180003 X-Rspamd-Server: rspam04 X-HE-Tag: 1768347341-502561 X-HE-Meta: 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 fcQNMmQn utB2QJ6ha/ufkWHbeQrNNaTO/WTTdV4xH7JgkPR1Xh9Kwsr7VlWEOJ2QqlnZi0wPZxS0XMerwku28Eu+8pRG5DM7YwWOMlxc4AS/xjSfs3RqkpcQ5ZZ4TI5Zanq52mj+bBCY+ZsHgshdCLdo4OKc1Gda5n2ja6o3AhMrpUvBRV9lEBVfSuAM1yC92v6/uNIOJjsO89JkdIUCeJDLmCeJ9u3ZWaujZTb1oAwl9EavyKm1HZ286D0M4Ahoo6PLZo5ByaZnzncltorua/PtfPrADPLNTFWSXoWVH11HscuEn4ClSlU72gwC6ocz9A+5itSbMyTlR5nEt550UI3BUHDybixgu/fzUdf8ejirMH/9nLEjcqmMAGnAbt7BdtfiWVGZLyVk1 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Alistair, On 2026-01-11 17:54, Alistair Popple wrote: > When mapping a p2pdma page the page reference count is initialised to > 1 prior to calling vm_insert_page(). This is to avoid vm_insert_page() > warning if the page refcount is zero. Prior to setting the page count > there is a check to ensure the page is currently free (ie. has a zero > reference count). > > However vm_insert_page() can fail. In this case the pages are freed > back to the genalloc pool, but that does not reset the page refcount. > So a future allocation of the same page will see the elevated page > refcount from the previous set_page_count() call triggering the > VM_WARN_ON_ONCE_PAGE checking that the page is free. > > Fix this by resetting the page refcount back to zero using > set_page_count(). Note that put_page() is not used because that > would result in freeing the page twice due to implicitly calling > p2pdma_folio_free(). > > Fixes: b7e282378773 ("mm/mm_init: move p2pdma page refcount initialisation to p2pdma") > Signed-off-by: Alistair Popple I had time today to pull out some old hardware and run this patch through my old p2pdma smoke tests. I don't think the tests exercise the change, but it looks correct to me on review. Reviewed-by: Logan Gunthorpe Thanks for the fix! Logan