pipe: Fix memory leaks in create_pipe_files()

Calling pipe2() with O_NOTIFICATION_PIPE could results in memory
leaks unless watch_queue_init() is successful.

        In case of watch_queue_init() failure in pipe2() we are left
with inode and pipe_inode_info instances that need to be freed.  That
failure exit has been introduced in commit c73be61ced ("pipe: Add
general notification queue support") and its handling should've been
identical to nearby treatment of alloc_file_pseudo() failures - it
is dealing with the same situation.  As it is, the mainline kernel
leaks in that case.

        Another problem is that CONFIG_WATCH_QUEUE and !CONFIG_WATCH_QUEUE
cases are treated differently (and the former leaks just pipe_inode_info,
the latter - both pipe_inode_info and inode).

        Fixed by providing a dummy wacth_queue_init() in !CONFIG_WATCH_QUEUE
case and by having failures of wacth_queue_init() handled the same way
we handle alloc_file_pseudo() ones.

Fixes: c73be61ced ("pipe: Add general notification queue support")
Signed-off-by: Qian Cai <cai@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/watch_queue.h

@@ -122,6 +122,12 @@ static inline void remove_watch_list(struct watch_list *wlist, u64 id)
  */
 #define watch_sizeof(STRUCT) (sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT)
 
+#else
+static inline int watch_queue_init(struct pipe_inode_info *pipe)
+{
+	return -ENOPKG;
+}
+
 #endif
 
 #endif /* _LINUX_WATCH_QUEUE_H */