Infinity loop when run "doveadm quota get -A" from Dovecot Director with 500 users

[Aki Tuomi]

Thanks for the patch, we'll take a look at it. 
Aki

> On 29/01/2021 04:49 Duc Anh Do <doducanh2710 at gmail.com> wrote:
> 
> 
> Hi all,
> 
> Because I think this is a race condition so instead of using only one current_ioloop:
>   * I create ioloop for each Backend in the list of Director
>   * I think connections from aDirector to same Backend are synchronous so I don't create ioloop for each connection
>   * I think ioloop must be destroyed in correct order so I use a linked list to manage them, create then push and pop then destroy (sorry, I don't know any existing structure in source of Dovecot that I can re-use)
> I tested my patch with both "doveadm quota get -A" and "doveadm quota get -u xxx" many times. No error occurs (timeout leak, segment fault... etc).
> If you are interested in my patch, any comment is highly appreciated. I modified source files which might be shared with other doveadm commands so I'm not sure it's safe 100%.
> 
> Thanks,
> Anh Do
> 
> 
> On Wed, 27 Jan 2021 at 16:20, Duc Anh Do <doducanh2710 at gmail.com> wrote:
> > Hi all,
> > 
> > I have one Dovecot Director, two Dovecot Backends and one LDAP server with about 500 users. I would like to run doveadm quota get -A from the Director.
> > In each Backend, there is no problem when run the command:
> > # doveadm quota get -A
> > user1 User quota STORAGE 0 1048576000000000 0
> > user1 User quota MESSAGE 0 - 0
> > …
> > user500 User quota STORAGE 0 1048576000000000 0
> > user500 User quota MESSAGE 0 - 0
> > 
> > However, when I run from the Director, the command might stuck in an infinity loop (I have to terminate to quit):
> > # doveadm quota get -A
> > user1 User quota STORAGE 0 1048576000000000 0
> > user1 User quota MESSAGE 0 - 0
> > …
> > user49 User quota STORAGE 0 1048576000000000 0
> > user49 User quota MESSAGE 0 - 0
> > user66 User quota STORAGE 0 1048576000000000 0
> > user66 User quota MESSAGE 0 - 0
> > ^Cdoveadm(user86): Error: doveadm server failure
> > doveadm: Error: Failed to iterate through some users
> > doveadm: Error: backend2.local:24245: Command quota get failed for user53: EOF
> > doveadm: Error: backend1.local:24245: Command quota get failed for user66: EOF
> > doveadm: Error: Aborted
> > 
> > This problem occurs in both Dovecot 2.2.36 and Dovecot 2.3.11, 2.3.13 (I build Dovecot from source). It's ok for me to get quota of one user from the Director:
> > # doveadm quota get -u user1
> > Quota name Type Value Limit %
> > User quota STORAGE 0 1048576000000000 0
> > User quota MESSAGE 0 - 0
> > And if there's only one Backend,doveadm quota get -A from the Director works well too.
> > 
> > After investigating, I found the infinity loop:
> > File src/doveadm/doveadm-mail-server.c:
> > static void doveadm_server_flush_one(struct doveadm_server *server)
> > {
> >  unsigned int count = array_count(&server->queue);
> > 
> >  do {
> >  io_loop_run(current_ioloop);
> >  } while (array_count(&server->queue) == count &&
> >  doveadm_server_have_used_connections(server) &&
> >  !DOVEADM_MAIL_SERVER_FAILED());
> > }
> > 
> > In case there're many Backends, I see only global variable current_ioloop is used to notify in the callback function. Might this be a race condition?
> > I understand there's a workaround to do my work:
> > 
> >   * Run doveadm user '*' to get all users
> >   * Loop through all users and run doveadm quota get -u xxx
> > 
> > Thanks,
> > Anh Do
> 
> 
> -- 
> 
> Thanks,
> Duc Anh
> ----------------------------------------------------------------------------------------------------
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