powerpc/mm: bail out early when flushing TLB page

MMU_NO_CONTEXT is conditionally defined as 0 or (unsigned int)-1. However,
in __flush_tlb_page() a corresponding variable is only tested for open
coded 0, which can cause NULL pointer dereference if `mm' argument was
legitimately passed as such.

Bail out early in case the first argument is NULL, thus eliminate confusion
between different values of MMU_NO_CONTEXT and avoid disabling and then
re-enabling preemption unnecessarily.

Signed-off-by: Arseny Solokha <asolokha@kb.kras.ru>
Signed-off-by: Scott Wood <scottwood@freescale.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/arch/powerpc/mm/tlb_nohash.c b/arch/powerpc/mm/tlb_nohash.c
index f38ea4df6a85..ab0616b0e6c2 100644
--- a/arch/powerpc/mm/tlb_nohash.c
+++ b/arch/powerpc/mm/tlb_nohash.c
@@ -284,8 +284,11 @@ void __flush_tlb_page(struct mm_struct *mm, unsigned long vmaddr,
         struct cpumask *cpu_mask;
         unsigned int pid;
 
+        if (unlikely(!mm))
+                return;
+
         preempt_disable();
-        pid = mm ? mm->context.id : 0;
+        pid = mm->context.id;
         if (unlikely(pid == MMU_NO_CONTEXT))
                 goto bail;
         cpu_mask = mm_cpumask(mm);