linux-kernel - Re: [PATCH] tracing: tprobe-events: Fix to clean up tprobe correctly when module unload

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Message-ID: <20250307122000.3087782f@gandalf.local.home>
Date: Fri, 7 Mar 2025 12:20:00 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing: tprobe-events: Fix to clean up tprobe
 correctly when module unload

On Thu,  6 Mar 2025 15:21:44 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> When unloading module, the tprobe events are not correctly cleaned
> up. Thus it becomes `fprobe-event` and never be enabled again even
> if loading the same module again.
> 
> For example;
> 
>  # cd /sys/kernel/tracing
>  # modprobe trace_events_sample
>  # echo 't:my_tprobe foo_bar' >> dynamic_events
>  # cat dynamic_events
> t:tracepoints/my_tprobe foo_bar
>  # rmmod trace_events_sample
>  # cat dynamic_events
> f:tracepoints/my_tprobe foo_bar
> 
> As you can see, the second time my_tprobe starts with 'f' instead
> of 't'.
> 
> This cleans up (unregister) the tprobe events when module is
> unloaded.

After applying this, I tried it out:

 # cd /sys/kernel/tracing
 # modprobe trace_events_sample
 # echo 't:my_tprobe foo_bar a=$arg1' > dynamic_events
 # echo 1 > events/tracepoints/enable
[wait]
 # echo 0 > events/tracepoints/enable
 # cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 13/13   #P:8
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
    event-sample-1041    [005] ...1.  1957.632897: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1958.656935: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1959.680883: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1960.704855: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1961.728977: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1962.751822: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1963.776834: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1964.800748: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1965.824788: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1966.848789: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1967.872902: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1968.896754: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1969.920737: my_tprobe: (__probestub_foo_bar+0x4/0x20 [trace_events_sample]) a=0xffffffffc006c186
 # rmmod trace_events_sample
 # cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 13/13   #P:8
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
    event-sample-1041    [005] ...1.  1957.632897: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1958.656935: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1959.680883: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1960.704855: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1961.728977: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1962.751822: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1963.776834: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1964.800748: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1965.824788: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1966.848789: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1967.872902: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1968.896754: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1969.920737: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186

 # modprobe trace_events_sample
 # echo 1 > events/tracepoints/enable
 # cat trace
# tracer: nop
#
# entries-in-buffer/entries-written: 13/13   #P:8
#
#                                _-----=> irqs-off/BH-disabled
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| / _-=> migrate-disable
#                              |||| /     delay
#           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
#              | |         |   |||||     |         |
    event-sample-1041    [005] ...1.  1957.632897: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1958.656935: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1959.680883: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1960.704855: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1961.728977: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1962.751822: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1963.776834: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1964.800748: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1965.824788: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1966.848789: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1967.872902: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1968.896754: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186
    event-sample-1041    [005] ...1.  1969.920737: my_tprobe: (0xffffffffc00620b4) a=0xffffffffc006c186

Tracing doesn't restart.

-- Steve