Re: (ITS#7167) regression, ldap_result() returns -1

[hyc@symas.com]

Howard Chu wrote:
> jvcelak@redhat.com wrote:
>> Full_Name: Jan Vcelak
>> Version: 2.4.29
>> OS: Linux
>> URL: ftp://ftp.openldap.org/incoming/
>> Submission from: (NULL) (209.132.186.34)
>>
>>
>> There is a possible regression caused by
>> 06ec9f1db2bb9dc304a4adcd0d0506203cf9e6b6.
>>
>> SSSD's event loop listens for events on a file descriptor retrieved using
>> ber_sockbuf_ctrl(sb, LBER_SB_OPT_GET_FD,&ber_fd). If there are some data to be
>> read, processing using ldap_result is triggered. (Internally, tevent from Samba
>> project is used, which uses epoll.) But sometimes, ldap_result() returns -1
>> error code. It seems that the descriptor is marked as readable untimely.
>>
>> This problem is not present with OpenLDAP 2.4.26, it appears with all future
>> versions. When the mentioned commit is reverted, everything works well.
>>
>> Original report in our Bugzilla:
>> https://bugzilla.redhat.com/show_bug.cgi?id=771484
>
> Thanks for the report and the detailed investigation, but this sounds to me
> like a kernel bug. We expect select/epoll/whatever to only return that a
> descriptor is readable if it actually is readable. (Gosh, who'dathunkit.) If
> not, then these syscalls are not behaving as documented/designed.

By the way, the patch in question was due to ITS#7035; you should read that 
ITS for the motivation behind this change.

-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/