> On 13 Jan 2021, at 21:24, Pierre Rogier <progier@xxxxxxxxxx> wrote: > > Thank you Willian, > So far your scenario (entry found when reading base entry but no more existing when computing the candidates) is the only one that matches the symptoms. It's a scenario we will need to fix via your BE work because of the MVCC transaction model that LMDB will force us to adopt :) > And that triggered a thought: > We cannot do anything for SUBTREE and ONE_LEVEL searches > because the fact that the base entry id is not in the candidate may be normal > but IMHO we should improve the BASE search case. > In this case the candidate list is directly set to the base entry id > ==> if the candidate entry (in ldbm_back_next_search_entry) is not found and the scope is BASE then we should return a LDAP_NO_SUCH_ENTRY error .. I suspect that Mark has seen this email and submitted a PR to resolve this exact case :) > > Pierre > > > On Wed, Jan 13, 2021 at 1:45 AM William Brown <wbrown@xxxxxxx> wrote: > Hey there, > > https://github.com/389ds/389-ds-base/pull/4525/files > > I had a look and I can see a few possible contributing factors, but without a core and the exact state I can't be sure if this is correct. It's all just hypothetical from reading the code. > > > The crash is in deref_do_deref_attr() which is called as part of deref_pre_entry(). This is the SLAPI_PLUGIN_PRE_ENTRY_FN which is called by "./ldap/servers/slapd/result.c:1488: rc = plugin_call_plugins(pb, SLAPI_PLUGIN_PRE_ENTRY_FN);" > > > I think what's important here is that the search is conducted in ./ldap/servers/slapd/opshared.c:818 rc = (*be->be_search)(pb); Is *not* in a transaction. That means that while the single search in be_search() is consistent due to an implied transaction, the subsequent search in deref_pre_entry() is likely conducted in a seperate transaction. This allows for other operations to potentially interleave and cause changes - modrdn or delete would certainly be candidates to cause a DN to be remove between these two points. It would be extremely hard to reproduce as a race condition of course. > > > A question you asked is why don't we get a "no such entry" error or similar? I think that this is because build_candidate_list in ldbm_search.c doesn't actually create an error if the base_candidates list is empty, because an IDL is allocated with a value of 0 (no matching entries). this allows the search to proceed, and there are no errors, and the result set is set to NULL with size 0. I can't see where LDAP_NO_SUCH_OBJECT is set in this process, but without looking further into it, my suspicion is that entries of size 0 WONT return an error condition to internal_search_pb, so it's valid for this to be empty. > > Anyway, again, this is just reading the code for 20 minutes, and is not a complete in depth investigation, but maybe it's some ideas about what happened? > > Hope it helps :) > > > > — > Sincerely, > > William Brown > > Senior Software Engineer, 389 Directory Server > SUSE Labs, Australia > _______________________________________________ > 389-devel mailing list -- 389-devel@xxxxxxxxxxxxxxxxxxxxxxx > To unsubscribe send an email to 389-devel-leave@xxxxxxxxxxxxxxxxxxxxxxx > Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: https://lists.fedoraproject.org/archives/list/389-devel@xxxxxxxxxxxxxxxxxxxxxxx > > > -- > -- > > 389 Directory Server Development Team > _______________________________________________ > 389-devel mailing list -- 389-devel@xxxxxxxxxxxxxxxxxxxxxxx > To unsubscribe send an email to 389-devel-leave@xxxxxxxxxxxxxxxxxxxxxxx > Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ > List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines > List Archives: https://lists.fedoraproject.org/archives/list/389-devel@xxxxxxxxxxxxxxxxxxxxxxx — Sincerely, William Brown Senior Software Engineer, 389 Directory Server SUSE Labs, Australia _______________________________________________ 389-devel mailing list -- 389-devel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to 389-devel-leave@xxxxxxxxxxxxxxxxxxxxxxx Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/389-devel@xxxxxxxxxxxxxxxxxxxxxxx
