Re: [PATCH] tracing: Add task_prctl_unknown tracepoint

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 5 Nov 2024 17:53:53 +0100
Marco Elver <elver@google.com> wrote:

> > > +/**
> > > + * task_prctl_unknown - called on unknown prctl() option
> > > + * @task:    pointer to the current task
> > > + * @option:  option passed
> > > + * @arg2:    arg2 passed
> > > + * @arg3:    arg3 passed
> > > + * @arg4:    arg4 passed
> > > + * @arg5:    arg5 passed
> > > + *
> > > + * Called on an unknown prctl() option.
> > > + */
> > > +TRACE_EVENT(task_prctl_unknown,
> > > +
> > > +     TP_PROTO(struct task_struct *task, int option, unsigned long arg2, unsigned long arg3,
> > > +              unsigned long arg4, unsigned long arg5),
> > > +
> > > +     TP_ARGS(task, option, arg2, arg3, arg4, arg5),
> > > +
> > > +     TP_STRUCT__entry(
> > > +             __field(        pid_t,          pid             )  
> >
> > Why record the pid that is already recorded by the event header?  
> 
> To keep in style with the other "task" tracepoints above. I can
> certainly do without - it does seem unnecessary.

Hmm, new_task, pid is different than the creator. But rename is pointless
to record pid. I would get rid of it here, especially since it also creates
a hole in the event (three int fields followed by a long).

> 
> To cleanup, do we want to remove "pid=" from the other tracepoints in
> this file as well (in another patch). Or does this potentially break
> existing users?

We can't from task_newtask as that's the pid of the task that's being
created. In other words, it's very relevant. The task_rename could have its
pid field dropped.

> 
> > > +             __string(       comm,           task->comm      )  
> >
> > I'm also surprised that the comm didn't show in the trace_pipe.  
> 
> Any config options or tweaks needed to get it to show more reliably?
> 
> > I've
> > updated the code so that it should usually find it. But saving it here may
> > not be a big deal.  

How did you start it? Because it appears reliable for me.

-- Steve