LTTng » LTTng-tools

Look like a race between the consumerd cleanup and the cleanup from sessiond.

Using lsmod we can see that there is no more refs on lttng_ring_buffer_metadata_client and it's easily removed with modprob by hand.

/sys/kernel/debug/tracing/modules give a way to track who is triggering modules_get and modules_put for lttng_ring_buffer_metadata_client (via filter).

        modprobe-13671 [002] .... 93370.022587: module_load: lttng_ring_buffer_client_discard OX
        modprobe-13671 [002] .... 93370.023329: module_put: lttng_ring_buffer_client_discard call_site=SyS_finit_module refcnt=2
  lttng-sessiond-13767 [002] .... 93377.718143: module_get: lttng_ring_buffer_client_discard call_site=lttng_channel_create [lttng_tracer] refcnt=3
  lttng-sessiond-13767 [002] .... 93377.722421: module_get: lttng_ring_buffer_client_discard call_site=_channel_create [lttng_ring_buffer_client_discard] refcnt=4
  lttng-sessiond-13661 [000] .... 93384.156345: module_put: lttng_ring_buffer_client_discard call_site=_lttng_channel_destroy [lttng_tracer] refcnt=1
 lttng-consumerd-13785 [002] .... 93384.394481: module_put: lttng_ring_buffer_client_discard call_site=release_priv_ops [lttng_ring_buffer_client_discard] refcnt=5

Looks like consumerd and sessiond release lttng_ring_buffer_client_discard on cleanup. If we break while removing the modules and assuring that consumerd release before the modules removal everything works fine.

Let's see where we can go from there. Any thought?