From 83014d82a1100abc89f7712ad67c3e5accaddc43 Mon Sep 17 00:00:00 2001 From: Alistair Popple Date: Mon, 12 Jan 2026 11:54:40 +1100 Subject: [PATCH] PCI/P2PDMA: Reset page reference count when page mapping fails 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 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 Signed-off-by: Bjorn Helgaas Reviewed-by: Logan Gunthorpe Acked-by: Balbir Singh Link: https://patch.msgid.link/20260112005440.998543-1-apopple@nvidia.com --- drivers/pci/p2pdma.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c index dd64ec830fdd..79a414fd6623 100644 --- a/drivers/pci/p2pdma.c +++ b/drivers/pci/p2pdma.c @@ -152,6 +152,13 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj, ret = vm_insert_page(vma, vaddr, page); if (ret) { gen_pool_free(p2pdma->pool, (uintptr_t)kaddr, len); + + /* + * Reset the page count. We don't use put_page() + * because we don't want to trigger the + * p2pdma_folio_free() path. + */ + set_page_count(page, 0); percpu_ref_put(ref); return ret; } -- 2.47.3