linux-kernel - Re: [PATCH] tracing: Add task_prctl

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Message-ID: <CANpmjNNTcrk7KtsQAdGVPmcOkiy446VmD-Y=YqxoUx+twTiOwA@mail.gmail.com>
Date: Tue, 5 Nov 2024 18:22:36 +0100
From: Marco Elver <elver@...gle.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Kees Cook <keescook@...omium.org>, Masami Hiramatsu <mhiramat@...nel.org>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org, 
	linux-trace-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>, 
	kasan-dev@...glegroups.com
Subject: Re: [PATCH] tracing: Add task_prctl_unknown tracepoint

On Tue, 5 Nov 2024 at 18:02, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 5 Nov 2024 17:53:53 +0100
> Marco Elver <elver@...gle.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.

Ack - will do.

> >
> > > > +             __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.

Very normally from bash. Maybe my env is broken in other ways, I'll
dig a little.