[PATCH] powerpc/mm: add sanity check to avoid null pointer dereference

[Defang Bo]

Similar to commit<0dc294f717d4>("powerpc/mm: bail out early when flushing TLB 
page"),
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 <bodef...@126.com>
---
 arch/powerpc/mm/nohash/tlb.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/mm/nohash/tlb.c b/arch/powerpc/mm/nohash/tlb.c
index 5872f69..1d89335 100644
--- a/arch/powerpc/mm/nohash/tlb.c
+++ b/arch/powerpc/mm/nohash/tlb.c
@@ -192,6 +192,9 @@ void local_flush_tlb_mm(struct mm_struct *mm)
 {
        unsigned int pid;
 
+       if (WARN_ON(!mm))
+               return;
+
        preempt_disable();
        pid = mm->context.id;
        if (pid != MMU_NO_CONTEXT)
@@ -205,8 +208,11 @@ void __local_flush_tlb_page(struct mm_struct *mm, unsigned 
long vmaddr,
 {
        unsigned int pid;
 
+       if (WARN_ON(!mm))
+               return;
+
        preempt_disable();
-       pid = mm ? mm->context.id : 0;
+       pid = mm->context.id;
        if (pid != MMU_NO_CONTEXT)
                _tlbil_va(vmaddr, pid, tsize, ind);
        preempt_enable();
@@ -268,6 +274,9 @@ void flush_tlb_mm(struct mm_struct *mm)
 {
        unsigned int pid;
 
+       if (WARN_ON(!mm))
+               return;
+
        preempt_disable();
        pid = mm->context.id;
        if (unlikely(pid == MMU_NO_CONTEXT))
-- 
2.7.4