new helper: ihold()

Clones an existing reference to inode; caller must already hold one.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/futex.c

@@ -169,7 +169,7 @@ static void get_futex_key_refs(union futex_key *key)
 
 	switch (key->both.offset & (FUT_OFF_INODE|FUT_OFF_MMSHARED)) {
 	case FUT_OFF_INODE:
-		atomic_inc(&key->shared.inode->i_count);
+		ihold(key->shared.inode);
 		break;
 	case FUT_OFF_MMSHARED:
 		atomic_inc(&key->private.mm->mm_count);