[PATCH 6.19 325/781] PCI/P2PDMA: Fix p2pmem_alloc_mmap() warning condition

Greg Kroah-Hartman
2026-02-25T01:32:53Z

From: Hou Tao <houtao1@huawei.com>

[ Upstream commit cb500023a75246f60b79af9f7321d6e75330c5b5 ]

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@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Link: https://patch.msgid.link/20251220040446.274991-3-houtao@huaweicloud.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 218c1f5252b66..dd64ec830fdd4 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) {
--
2.51.0