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

[Duc Anh Do]

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
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