Not all pages may apply to pgtable check. One example is ZONE_DEVICE
pages: they map PFNs directly, and they don't allocate page_ext at all even
if there's struct page around. One may reference devm_memremap_pages().
When both ZONE_DEVICE and page-table-check enabled, then try to map some
dax memories, one can trigger kernel bug constantly now when the kernel was
trying to inject some pfn maps on the dax device:
kernel BUG at mm/page_table_check.c:55!
While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for page
fault resolutions, skip all the checks if page_ext doesn't even exist in
pgtable checker, which applies to ZONE_DEVICE but maybe more.
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---
mm/page_table_check.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/page_table_check.c b/mm/page_table_check.c
index 4169576bed72..509c6ef8de40 100644
--- a/mm/page_table_check.c
+++ b/mm/page_table_check.c
@@ -73,6 +73,9 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt)
page = pfn_to_page(pfn);
page_ext = page_ext_get(page);
+ if (!page_ext)
+ return;
+
BUG_ON(PageSlab(page));
anon = PageAnon(page);
@@ -110,6 +113,9 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt,
page = pfn_to_page(pfn);
page_ext = page_ext_get(page);
+ if (!page_ext)
+ return;
+
BUG_ON(PageSlab(page));
anon = PageAnon(page);
@@ -140,7 +146,10 @@ void __page_table_check_zero(struct page *page, unsigned int order)
BUG_ON(PageSlab(page));
page_ext = page_ext_get(page);
- BUG_ON(!page_ext);
+
+ if (!page_ext)
+ return;
+
for (i = 0; i < (1ul << order); i++) {
struct page_table_check *ptc = get_page_table_check(page_ext);
--
2.45.0
