[SPARC64]: flush_ptrace_access() needs preemption disable.

Based upon a report by Mariusz Kozlowski.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc64/kernel/ptrace.c

@@ -70,6 +70,8 @@ void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
 	if (tlb_type == hypervisor)
 		return;
 
+	preempt_disable();
+
 #ifdef DCACHE_ALIASING_POSSIBLE
 	/* If bit 13 of the kernel address we used to access the
 	 * user page is the same as the virtual address that page
@@ -108,6 +110,8 @@ void flush_ptrace_access(struct vm_area_struct *vma, struct page *page,
 		for (; start < end; start += icache_line_size)
 			flushi(start);
 	}
+
+	preempt_enable();
 }
 
 enum sparc_regset {