Re: [PATCH] tracing: Reset the function filter after completing trampoline/graph selftest

[Li Huafei]

Hi Steve,

On 2022/4/26 6:58, Steven Rostedt wrote:
> On Mon, 18 Apr 2022 15:39:58 +0800
> Li Huafei <lihuafei1@xxxxxxxxxx> wrote:
>
> > The direct trampoline and graph coexistence test sets global_ops to
> > trace only 'trace_selftest_dynamic_test_func', but does not reset it
> > after the test is completed, resulting in the function filter being set
> > already after the system starts. Although it can be reset through the
> > tracefs interface, it is more or less confusing to the user, and we
> > should reset it to trace all functions after the trampoline/graph test
> > completes.
> >
> > Fixes: 130c08065848 ("tracing: Add trampoline/graph selftest")
> > Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
> > ---
> >   kernel/trace/trace_selftest.c | 12 ++++++++----
> >   1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
> > index abcadbe933bb..e89f72571f8e 100644
> > --- a/kernel/trace/trace_selftest.c
> > +++ b/kernel/trace/trace_selftest.c
> > @@ -866,12 +866,12 @@ trace_selftest_startup_function_graph(struct tracer *trace,
> >   	ret = register_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
> >   				     (unsigned long) trace_direct_tramp);
> >   	if (ret)
> > -		goto out;
> > +		goto reset_filter;
> >   
> >   	ret = register_ftrace_graph(&fgraph_ops);
> >   	if (ret) {
> >   		warn_failed_init_tracer(trace, ret);
> > -		goto out;
> > +		goto reset_filter;
> >   	}
> >   
> >   	DYN_FTRACE_TEST_NAME();
> > @@ -887,14 +887,18 @@ trace_selftest_startup_function_graph(struct tracer *trace,
> >   	ret = unregister_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
> >   				       (unsigned long) trace_direct_tramp);
> >   	if (ret)
> > -		goto out;
> > +		goto reset_filter;
> >   
> >   	tracing_start();
> >   
> >   	if (!ret && !count) {
> >   		ret = -1;
> > -		goto out;
> > +		goto reset_filter;
> No need for all the 'goto reset_filter', if this function fails, then the
> tracer is disabled, and there's no reason to clear the filter. In fact, it
Thank you for the review. I see that we will disable function_graph tracer:

     /* Stop it if we failed */
     if (ret)
           ftrace_graph_stop();

But there is no function tracer disabled. Am I missing something that 
would disable the function tracer?


> may cause a crash (because something bad happened).

Yes, so should we kill ftrace when the function_graph test fails?

Thanks,
Huafei

> -- Steve
>
>
> >   	}
> > +
> > +reset_filter:
> > +	/* Enable tracing on all functions again */
> > +	ftrace_set_global_filter(NULL, 0, 1);
> >   #endif
> >   
> >   	/* Don't test dynamic tracing, the function tracer already did */
> .