Bug #878
closed
lttng-sessiond cannot unload lttng-modules when live session exists
Added by Mathieu Desnoyers about 9 years ago.
Updated over 8 years ago.
Assignee:
Jonathan Rajotte Julien
Description
After the following set of commands:
lttng-sessiond (as root)
lttng create --live; lttng enable-channel -k test; lttng start
If we CTRL-C lttng-sessiond, this appears:
^CError: Unable to remove module lttng-ring-buffer-client-discard
Error: Unable to remove module lttng-lib-ring-buffer
Error: Unable to remove module lttng-tracer
It appears there is still a refcount held by sessiond when we try to remove the modules in this scenario. It could be a file that should have been closed but has not.
- Assignee set to Jonathan Rajotte Julien
- Status changed from New to Confirmed
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?
- Status changed from Confirmed to In Progress
- Status changed from In Progress to Feedback
- Target version set to 2.7
- Status changed from Feedback to Resolved
- % Done changed from 0 to 100
Applied in changeset tools|commit:4e4714cb244d7ace4f4a462a3923066fd4760669.
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