uml: fix mm_context memory leak

[ Spotted by Miklos ]

Fix a memory leak in init_new_context.  The struct page ** buffer allocated
for install_special_mapping was never recorded, and thus leaked when the
mm_struct was freed.  Fix it by saving the pointer in mm_context_t and freeing
it in arch_exit_mmap.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/include/um_mmu.h b/arch/um/include/um_mmu.h
index 82865fc..f575ff9 100644
--- a/arch/um/include/um_mmu.h
+++ b/arch/um/include/um_mmu.h
@@ -13,6 +13,7 @@
 typedef struct mm_context {
 	struct mm_id id;
 	struct uml_ldt ldt;
+	struct page **stub_pages;
 } mm_context_t;
 
 extern void __switch_mm(struct mm_id * mm_idp);