[PATCH] powerpc/mm: avoid null pointer dereference in flush_tlb_mm

[Defang Bo]

Similar to commit<0dc294f7>, there should be a check for 'mm' to prevent Null pointer dereference in case of 'mm' argument was legitimately passed.

Signed-off-by: Defang Bo <bodefang at 126.com>
---
 arch/powerpc/mm/nohash/tlb.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/powerpc/mm/nohash/tlb.c b/arch/powerpc/mm/nohash/tlb.c
index 5872f69..09796c9 100644
--- a/arch/powerpc/mm/nohash/tlb.c
+++ b/arch/powerpc/mm/nohash/tlb.c
@@ -268,6 +268,9 @@ void flush_tlb_mm(struct mm_struct *mm)
 {
 	unsigned int pid;
 
+	if (unlikely(!mm))
+		return;
+
 	preempt_disable();
 	pid = mm->context.id;
 	if (unlikely(pid == MMU_NO_CONTEXT))
-- 
2.7.4