From: Ingo Molnar <mingo@elte.hu>

Teach special (recursive) locking code to the lock validator.  Has no effect
on non-lockdep kernels.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 kernel/fork.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff -puN kernel/fork.c~lockdep-annotate-mmap_sem kernel/fork.c
--- a/kernel/fork.c~lockdep-annotate-mmap_sem
+++ a/kernel/fork.c
@@ -194,7 +194,10 @@ static inline int dup_mmap(struct mm_str
 
 	down_write(&oldmm->mmap_sem);
 	flush_cache_mm(oldmm);
-	down_write(&mm->mmap_sem);
+	/*
+	 * Not linked in yet - no deadlock potential:
+	 */
+	down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
 
 	mm->locked_vm = 0;
 	mm->mmap = NULL;
_