flock: blocked processes are not interesting for us (v2)

All out processes are stopped in a moment, when file locks are
collected, so they can't to wait any locks.

Here is a proof of this theory:
[root@avagin-fc19-cr ~]# flock xxx sleep 1000 &
[1] 23278
[root@avagin-fc19-cr ~]# flock xxx sleep 1000 &
[2] 23280
[root@avagin-fc19-cr ~]# cat /proc/locks
1: FLOCK  ADVISORY  WRITE 23278 08:03:280001 0 EOF
1: -> FLOCK  ADVISORY  WRITE 23280 08:03:280001 0 EOF
[root@avagin-fc19-cr ~]# gdb -p 23280
(gdb) ^Z
[3]+  Stopped                 gdb -p 23280
[root@avagin-fc19-cr ~]# cat /proc/locks
1: FLOCK  ADVISORY  WRITE 23278 08:03:280001 0 EOF

Currently criu can dump nothing, if we have one process which is
waiting a lock. I don't see any reason to do this.

v2: typo fix

Cc: Qiang Huang <h.huangqiang@huawei.com>
Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

proc_parse.c

@@ -1536,6 +1536,12 @@ int parse_file_locks(void)
 			goto err;
 		}
 
+		pr_info("lockinfo: %lld:%d %x %d %02x:%02x:%ld %lld %s\n",
+			fl->fl_id, fl->fl_kind, fl->fl_ltype,
+			fl->fl_owner, fl->maj, fl->min, fl->i_no,
+			fl->start, fl->end);
+
+
 		if (fl->fl_kind == FL_UNKNOWN) {
 			pr_err("Unknown file lock!\n");
 			ret = -1;
@@ -1543,35 +1549,25 @@ int parse_file_locks(void)
 			goto err;
 		}
 
-		if ((fl->fl_kind == FL_POSIX) &&
-				!pid_in_pstree(fl->fl_owner)) {
+		if (is_blocked) {
 			/*
-			 * We only care about tasks which are taken
-			 * into dump, so we only collect file locks
-			 * belong to these tasks.
+			 * All target processes are stopped in this moment and
+			 * can't wait any locks.
 			 */
+			pr_debug("Skip blocked processes\n");
 			xfree(fl);
 			continue;
 		}
 
-		pr_info("lockinfo: %lld:%d %x %d %02x:%02x:%ld %lld %s\n",
-			fl->fl_id, fl->fl_kind, fl->fl_ltype,
-			fl->fl_owner, fl->maj, fl->min, fl->i_no,
-			fl->start, fl->end);
-
-		if (is_blocked) {
+		if ((fl->fl_kind == FL_POSIX) &&
+				!pid_in_pstree(fl->fl_owner)) {
 			/*
-			 * Here the task is in the pstree.
-			 * If it is blocked on a flock, when we try to
-			 * ptrace-seize it, the kernel will unblock task
-			 * from flock and will stop it in another place.
-			 * So in dumping, a blocked file lock should never
-			 * be here.
+			 * We only care about tasks which are taken
+			 * into dump, so we only collect file locks
+			 * belong to these tasks.
 			 */
-			pr_perror("We have a blocked file lock!");
-			ret = -1;
 			xfree(fl);
-			goto err;
+			continue;
 		}
 
 		list_add_tail(&fl->list, &file_lock_list);