pid-namespaces-vs-locks-interaction

fcntl(F_GETLK,..) can return pid of process for not current pid namespace
(if process is belonged to the several namespaces).  It is true also for
pids in /proc/locks.  So correct behavior is saving pointer to the struct
pid of the process lock owner.

Signed-off-by: Vitaliy Gusev <vgusev@openvz.org>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

include/linux/fs.h

@@ -872,6 +872,7 @@ struct file_lock {
 	struct list_head fl_block;	/* circular list of blocked processes */
 	fl_owner_t fl_owner;
 	unsigned int fl_pid;
+	struct pid *fl_nspid;
 	wait_queue_head_t fl_wait;
 	struct file *fl_file;
 	unsigned char fl_flags;