/* permission checks */

/* If the process being read is separated by chroot from the reading process,
 * don't let the reader access the threads.
 */
static int proc_check_chroot(struct dentry *root, struct vfsmount *vfsmnt)

resolution: override for admin (CAP_CONTEXT)

http://vserver.13thfloor.at/Devel/PAT-2.0.2/delta-proc-fix01.diff
http://vserver.13thfloor.at/Devel/PAT-2.1.1/delta-proc-fix01.diff