mm: export use_mm/unuse_mm to modules

vhost net module wants to do copy to/from user from a kernel thread,
which needs use_mm. Export it to modules.
Acked-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

mm/mmu_context.c

@@ -5,6 +5,7 @@
 
 #include <linux/mm.h>
 #include <linux/mmu_context.h>
+#include <linux/module.h>
 #include <linux/sched.h>
 
 #include <asm/mmu_context.h>
@@ -37,6 +38,7 @@ void use_mm(struct mm_struct *mm)
 	if (active_mm != mm)
 		mmdrop(active_mm);
 }
+EXPORT_SYMBOL_GPL(use_mm);
 
 /*
  * unuse_mm
@@ -56,3 +58,4 @@ void unuse_mm(struct mm_struct *mm)
 	enter_lazy_tlb(mm, tsk);
 	task_unlock(tsk);
 }
+EXPORT_SYMBOL_GPL(unuse_mm);