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LIN7-4770 : CLONE - CLONE - XMU03: Lttng filtered tracepoint disabling error

Created: Sep 15, 2015    Updated: Sep 8, 2018
Resolved Date: Sep 17, 2015
Previous ID: LIN6-10346
Found In Version:
Fix Version:
Severity: Standard
Applicable for: Wind River Linux 7
Component/s: Userspace



While testing enabling and disabling tracepoints on XMU03 using lttng we found what seems to be a bug with lttng disable command. If one enables tracepoint using filtering per process, then enables tracepoint without a filter and then tries to disable that tracepoint, the ones enabled with filtering always stay enabled and we haven't found a way to disable them.

If I'm correct lttng currently doesn't support specifically disabling tracepoints using filters but I presume that if I try disabling a tracepoint (for all processes) even those enabled with filter should be disabled. Lttng also lists all tracepoints as disabled although tracing continues. This happens whether the traces are enabled through user application or with lttng shell command.

To reproduce:
first enable tracepoint with filter for process:
lttng enable-event my_provider:my_tracepoint --filter  '$ctx.procname == "my-process*"' --session session -u -c channel

then enable tracing for all processes:
lttng enable-event my_provider:my_tracepoint --session session -u -c channel

then try disabling tracepoint:
lttng disable-event --session session --channel channel --userspace my_provider:my_tracepoint

lttng list session gives:
my_provider:my_tracepoint (type: tracepoint) [disabled]
my_provider:my_tracepoint (type: tracepoint) [disabled] [with filter]

and traces for a filtered process will still be logging.

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