ABORT due to failing assertion

[smurfix]

1.6.9, two brokers with persistence=false retain_available=false.

Mai 21 18:12:30 pi-c3 mosquitto[7800]: Connecting bridge (step 1) upstream (10.107.0.90:51883)
Mai 21 18:12:30 pi-c3 mosquitto[7800]: Connecting bridge (step 2) upstream (10.107.0.90:51883)
Mai 21 18:12:30 pi-c3 mosquitto[7800]: mosquitto: /build/mosquitto-coWg4m/mosquitto-1.6.9/src/loop.c:730: loop_handle_reads_writes: Assertion `pollfds[context->pollfd_index].fd == context->sock' failed.
Mai 21 18:12:30 pi-c3 systemd[1]: mosquitto.service: Main process exited, code=killed, status=6/ABRT
Mai 21 18:12:30 pi-c3 systemd[1]: mosquitto.service: Failed with result 'signal'.

[ralight]

What platform are you building on, and what build options are you using? Is there anything else in your config file apart from the bridge and retain_available false?

[smurfix]

Log:

1590079596: mosquitto version 1.6.9 starting
1590079596: Config loaded from /etc/mosquitto/mosquitto.conf.
1590079596: Opening ipv4 listen socket on port 51883.
1590079596: Connecting bridge (step 1) dev (10.107.3.2:51883)
1590079596: Connecting bridge (step 2) dev (10.107.3.2:51883)
1590079596: Socket error on client local.dev, disconnecting.
1590079601: Connecting bridge (step 1) dev (10.107.3.2:51883)
[ death here ]

strace:

[pid 77380] write(8, "\0204\0\4MQTT\204.\0\5\0\3dev\0 $SYS/broker/connection/dev/state\0\0010", 54) = 54
[pid 77380] read(8, "", 1)              = 0

while the other side does (different bridge peer but same problem)

4281  rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
4281  read(8, "\20", 1)                 = 1
4281  read(8, "8", 1)                   = 1
4281  read(8, "\0\4MQTT\204,\0\5\0\5pi-f3\0\"$SYS/broker/connection/pi-f3/state\0\0010", 56) = 56
4281  clock_gettime(CLOCK_MONOTONIC, {tv_sec=1112514, tv_nsec=277688747}) = 0
4281  gettimeofday({tv_sec=1590079989, tv_usec=16567}, NULL) = 0
4281  gettimeofday({tv_sec=1590079989, tv_usec=16766}, NULL) = 0
4281  getpid()                          = 4281
4281  send(5, "<29>May 21 18:53:09 mosquitto[4281]: Socket error on client <unknown>, disconnecting.", 85, MSG_NOSIGNAL) = 85
4281  close(8)                          = 0

so apparently there are two bugs here:

• aborting a bridge connection causes the connecting server to die an ignoble death some time later
• when retain_available is off, that $SYS/…/state LWT message should be sent without retain

[smurfix]

Platform is Debian, I'm using their 1.6.9 packages. I can build a minimum reproducer with the current mosquitto master as soon as I finish the job which this bug has rudely interrupted. ;-)

[ralight]

Ok, I can reproduce it now thank you. This only occurs if epoll isn't being used and the Debian packages should absolutely definitely be using epoll, but they aren't.

[smurfix]

Right, they're using poll. I'll file a bug report.

On a related note: why the censored does mosquitto not sleep longer than 100msec? I'd like my computer to save power when nobody is talking to it …

[ralight]

There's probably no need, I'll do a new release 1.6.10 and fix the package at the same time.

100ms - it's just been like that forever. I suppose this could be raised to 1 second at most.

[smurfix]

Umm, but why is there a periodic timer anyway? Presumably the code could actually discover how long it should sleep, and then just wait that long.

[ralight]

It's just a matter of simplicity and available time to make changes. Having said that, some other changes I've been making would make this a good time to revisit it.