lib/test_hmm: fix garbage pfn and wrong direction in devmem fault debug

Move pr_debug() inside the `if (dpage)` block to avoid printing garbage
pfn for NULL dpage, and correct the direction label from "sys to dev" to
"dev to sys".

Link: https://lore.kernel.org/20260812092856.55296-1-liuqiangneo@163.com
Signed-off-by: Qiang Liu <liuqiang@kylinos.cn>
Assisted-by: Qoder:Qwen-3.8-MAX-Preview
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 6205fb3..7c4d10e 100644 (file)
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -1151,10 +1151,9 @@ static vm_fault_t dmirror_devmem_fault_alloc_and_copy(struct migrate_vma *args,
                if (!dpage && !order)
                        return VM_FAULT_OOM;
 
-               pr_debug("migrating from sys to dev pfn src: 0x%lx pfn dst: 0x%lx\n",
-                               page_to_pfn(spage), page_to_pfn(dpage));
-
                if (dpage) {
+                       pr_debug("migrating from dev to sys pfn src: 0x%lx pfn dst: 0x%lx\n",
+                                       page_to_pfn(spage), page_to_pfn(dpage));
                        lock_page(dpage);
                        *dst |= migrate_pfn(page_to_pfn(dpage));
                }