Re: Re: [PATCH 3/3] mm: mmap_lock: add ip to mmap_lock tracepoints

[Gang Li]

On 7/31/21 4:03 AM, Steven Rostedt wrote:
> Yes, synthetic events are just like normal events, and have triggers,
> stack traces, and do pretty much anything that another event can do.
>
> I'm just finishing up a libtracfs called tracefs_sql() (hopefully
> posting it today), that allows you to create a synthetic event via an
> SQL statement. But I don't think this is what you are looking for.
>
> What about using function tracing? Because the tracepoint is called
> from __mmap_lock* helper functions that function tracer can see, you
> can just do the following:
>
>   # trace-cmd start -e mmap_lock -p function -l '__mmap_lock_*'
>   # trace-cmd show
> [..]
>         trace-cmd-1840    [006] ....   194.576801: __mmap_lock_do_trace_start_locking <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576805: mmap_lock_start_locking: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
>
>         trace-cmd-1840    [006] ....   194.576806: __mmap_lock_do_trace_acquire_returned <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576807: mmap_lock_acquire_returned: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false success=true
>
>         trace-cmd-1840    [006] ....   194.576811: __mmap_lock_do_trace_released <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576812: mmap_lock_released: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
>
>         trace-cmd-1840    [006] ....   194.576815: __mmap_lock_do_trace_start_locking <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576816: mmap_lock_start_locking: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
>
>         trace-cmd-1840    [006] ....   194.576816: __mmap_lock_do_trace_acquire_returned <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576817: mmap_lock_acquire_returned: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false success=true
>
>         trace-cmd-1840    [006] ....   194.576820: __mmap_lock_do_trace_released <-do_user_addr_fault
>         trace-cmd-1840    [006] ...1   194.576821: mmap_lock_released: mm=000000006515cb1f memcg_path=/user.slice/user-0.slice/session-2.scope write=false
>
>
> This looks exactly like the robots you are looking for.
>
> -- Steve

I think this is exactly what I am looking for.
Thanks!