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

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Message-Id: <20251220040446.274991-3-houtao@huaweicloud.com>
Date: Sat, 20 Dec 2025 12:04:35 +0800
From: Hou Tao <houtao@...weicloud.com>
To: 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>,
	Logan Gunthorpe <logang@...tatee.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: [PATCH 02/13] PCI/P2PDMA: Fix the warning condition in p2pmem_alloc_mmap()

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>
---
 drivers/pci/p2pdma.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index 218c1f5252b6..dd64ec830fdd 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -147,7 +147,7 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj,
 		 * we have just allocated the page no one else should be
 		 * using it.
 		 */
-		VM_WARN_ON_ONCE_PAGE(!page_ref_count(page), page);
+		VM_WARN_ON_ONCE_PAGE(page_ref_count(page), page);
 		set_page_count(page, 1);
 		ret = vm_insert_page(vma, vaddr, page);
 		if (ret) {
-- 
2.29.2