[PATCH] mm/khugepaged: fix a tracepoint for error cases

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

Fix a potential NULL pointer dereference in trace_mm_khugepaged_scan_pmd()
when folio is NULL. This is possible if vm_normal_page() returned a NULL
page -- which is unlikely, but was hit in testing.

(The tracepoint in include/trace/events/huge_memory.h can already deal
with a NULL page.)

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>

---
Based on akpm/mm-unstable.

 mm/khugepaged.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index cc945c6ab3bd..eb7b019159d4 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1435,8 +1435,9 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		*mmap_locked = false;
 	}
 out:
-	trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenced,
-				     none_or_zero, result, unmapped);
+	trace_mm_khugepaged_scan_pmd(mm, folio ? &folio->page : NULL,
+				     writable, referenced, none_or_zero,
+				     result, unmapped);
 	return result;
 }
 

base-commit: e026356e4192ff5a52c1d535e6b9e3fa50def2c4
-- 
2.48.1