Locks created by flock() are associated with an open file description
This means that duplicate file descriptors (created by, for  example,
fork or  dup)  refer  to  the  same  lock.

Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>