rare assertion failure on syncprov-related test(s) on a busy machine

[erthink]

slap.2.log:

160817-00:12:55.692335_00752 syncprov_send_resp: LDAP_SYNC_MODIFY, olcDatabase={0}config,cn=config, to=001, 9661da4e-5a03-494d-958b-3ddb61ad7b07, (null)
160817-00:12:55.692342_00752 syncprov_state_ctrl: rid=002, LDAP_SYNC_MODIFY, (null), 9661da4e-5a03-494d-958b-3ddb61ad7b07, no-CSN
160817-00:12:55.692362_00752 => send_search_entry: conn 1003 dn="olcDatabase={0}config,cn=config"
160817-00:12:55.694878_00752 *** Backtrace by addr2line:
160817-00:12:55.750858_00752 (0) __ldap_assert_fail у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/globals.c:230
160817-00:12:55.762743_00752 (1) ber_int_sb_write у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/libraries/libreldap/sockbuf.c:459 (discriminator 1)
160817-00:12:55.763045_00752 (2) ber_flush2 у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/libraries/libreldap/io.c:254
160817-00:12:55.764399_00752 (3) send_ldap_ber у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/result.c:384
160817-00:12:55.767448_00752 (4) slap_send_search_entry у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/result.c:1471
160817-00:12:55.768915_00752 (5) syncprov_sendresp у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/overlays/syncprov.c:1147
160817-00:12:55.768932_00752 (6)  (внутристрочный) syncprov_playback_locked у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/overlays/syncprov.c:1182
160817-00:12:55.768938_00752 (7)  (внутристрочный) syncprov_playback_dequeue у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/servers/slapd/overlays/syncprov.c:1239
160817-00:12:55.771713_00752 (8) ldap_int_thread_pool_wrapper у /home/ly/tmp/ReOpenLDAP/@ci-buzz.pool/@1.local/src/libraries/libreldap/tpool.c:721
slapd: sockbuf.c:459: ber_int_sb_write: Проверочное утверждение «ldap: sb->sb_iod != ((void *)0)» не выполнено.