[bug report] powerpc/mm/radix: Avoid flushing the PWC on every flush_tlb_range

[Dan Carpenter]

Hello Benjamin Herrenschmidt,

This is a semi-automatic email about new static checker warnings.

The patch 424de9c6e3f8: "powerpc/mm/radix: Avoid flushing the PWC on 
every flush_tlb_range" from Jul 19, 2017, leads to the following 
Smatch complaint:

arch/powerpc/mm/tlb-radix.c:368 radix__flush_tlb_collapsed_pmd()
         error: we previously assumed 'mm' could be null (see line 362)

arch/powerpc/mm/tlb-radix.c
   361  
   362          pid = mm ? mm->context.id : 0;
                      ^^
Check for NULL.

   363          if (unlikely(pid == MMU_NO_CONTEXT))
   364                  goto no_context;
   365  
   366          /* 4k page size, just blow the world */
   367          if (PAGE_SIZE == 0x1000) {
   368                  radix__flush_all_mm(mm);
                                            ^^
Unchecked dereference.

   369                  return;
   370          }

regards,
dan carpenter