powerpc/mm: bail out early when flushing TLB page
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 <22bb72fdcc1d8e9f19486b14aec4ebf24e0ae48a@kb.kras.ru>
Signed-off-by: Scott Wood <b77916c2feab81a70245e7b5671f4f02730ebf64@freescale.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs