linux-kernel - Re: [PATCH] selftests/ftrace: Select an existing function in kprobe

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Date:   Tue, 9 Jul 2019 21:44:02 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Shuah Khan <shuahkhan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] selftests/ftrace: Select an existing function in
 kprobe_eventname test

On Mon, 8 Jul 2019 15:22:14 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 8 Jul 2019 16:10:29 -0300
> Thadeu Lima de Souza Cascardo <cascardo@...onical.com> wrote:
> 
> > On Fri, Mar 22, 2019 at 03:09:23PM -0400, Steven Rostedt wrote:
> > > From: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > > 
> > > Running the ftrace selftests on the latest kernel caused the
> > > kprobe_eventname test to fail. It was due to the test that searches for
> > > a function with at "dot" in the name and adding a probe to that.
> > > Unfortunately, for this test, it picked:
> > > 
> > >  optimize_nops.isra.2.cold.4
> > > 
> > > Which happens to be marked as "__init", which means it no longer exists
> > > in the kernel! (kallsyms keeps those function names around for tracing
> > > purposes)

Ouch!

> > > 
> > > As only functions that still exist are in the
> > > available_filter_functions file, as they are removed when the functions
> > > are freed at boot or module exit, have the test search for a function
> > > with ".isra." in the name as well as being in the
> > > available_filter_functions (if the file exists).

Hmm, OK. But I think this eventually fixed in kallsyms, by something like 
having [GONE] or [__init] flag for such symbols.

> > >   
> > 
> > This fixes a similar problem for me.
> > 
> > Tested-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
> 
> Masami, can you ack this, and Shuah, can you take it?

Yeah anyway,

Acked-by: Masami Hiramatsu <mhiramat@...nel.org>

Thank you!

> 
> Thanks!
> 
> -- Steve
> 
> > 
> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> > > ---
> > > diff --git a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> > > index 3fb70e01b1fe..3ff236719b6e 100644
> > > --- a/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> > > +++ b/tools/testing/selftests/ftrace/test.d/kprobe/kprobe_eventname.tc
> > > @@ -24,7 +24,21 @@ test -d events/kprobes2/event2 || exit_failure
> > >  
> > >  :;: "Add an event on dot function without name" ;:
> > >  
> > > -FUNC=`grep -m 10 " [tT] .*\.isra\..*$" /proc/kallsyms | tail -n 1 | cut -f 3 -d " "`
> > > +find_dot_func() {
> > > +	if [ ! -f available_filter_functions ]; then
> > > +		grep -m 10 " [tT] .*\.isra\..*$" /proc/kallsyms | tail -n 1 | cut -f 3 -d " "
> > > +		return;
> > > +	fi
> > > +
> > > +	grep " [tT] .*\.isra\..*" /proc/kallsyms | cut -f 3 -d " " | while read f; do
> > > +		if grep -s $f available_filter_functions; then
> > > +			echo $f
> > > +			break
> > > +		fi
> > > +	done
> > > +}
> > > +
> > > +FUNC=`find_dot_func | tail -n 1`
> > >  [ "x" != "x$FUNC" ] || exit_unresolved
> > >  echo "p $FUNC" > kprobe_events
> > >  EVENT=`grep $FUNC kprobe_events | cut -f 1 -d " " | cut -f 2 -d:`  
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>