Re: [PATCH] ftrace/selftest: Test combination of function_graph tracer and function profiler

[Steven Rostedt <rostedt@goodmis.org>]

On Wed, 21 Aug 2024 21:54:42 -0600
Shuah Khan <skhan@linuxfoundation.org> wrote:

> On 8/21/24 13:09, Steven Rostedt wrote:
> > From: Steven Rostedt <rostedt@goodmis.org>
> > 
> > Masami reported a bug when running function graph tracing then the
> > function profiler. The following commands would cause a kernel crash:
> > 
> >    # cd /sys/kernel/tracing/
> >    # echo function_graph > current_tracer
> >    # echo 1 > function_profile_enabled
> > 
> > In that order. Create a test to test this two to make sure this does not
> > come back as a regression.
> > 
> > Link: https://lore.kernel.org/172398528350.293426.8347220120333730248.stgit@devnote2
> > 
> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> > ---
> >   .../ftrace/test.d/ftrace/fgraph-profiler.tc   | 30 +++++++++++++++++++
> >   1 file changed, 30 insertions(+)
> >   create mode 100644 tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> > 
> > diff --git a/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> > new file mode 100644
> > index 000000000000..62d44a1395da
> > --- /dev/null
> > +++ b/tools/testing/selftests/ftrace/test.d/ftrace/fgraph-profiler.tc
> > @@ -0,0 +1,30 @@
> > +#!/bin/sh
> > +# SPDX-License-Identifier: GPL-2.0
> > +# description: ftrace - function profiler with function graph tracing
> > +# requires: function_profile_enabled set_ftrace_filter function_graph:tracer
> > +
> > +# The function graph tracer can now be run along side of the function
> > +# profiler. But there was a bug that caused the combination of the two
> > +# to crash. It also required the function graph tracer to be started
> > +# first.
> > +#
> > +# This test triggers that bug
> > +#
> > +# We need function_graph and profiling to to run this test
> > +
> > +fail() { # mesg
> > +    echo $1
> > +    exit_fail
> > +}
> > +
> > +echo "Enabling function graph tracer:"
> > +echo function_graph > current_tracer
> > +echo "enable profiler"
> > +
> > +# Older kernels do not allow function_profile to be enabled with
> > +# function graph tracer. If the below fails, mark it as unsupported
> > +echo 1 > function_profile_enabled || exit_unsupported
> > +
> > +sleep 1  
> 
> Any specific reason for this sleep 1 - can you add a comment on top?

We add sleep 1 in several locations of the ftrace selftests to let the
tracing run for a bit just to see if it triggers anything. Otherwise the
clean up can happen before anything gets traced. Although, it's highly
unlikely in this case, but still.

I could add a comment if you want of just:

# let it run for a bit
sleep 1


> > +
> > +exit 0  
> 
> Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
> 
> Let me know if you would like v2 for this to be taken through my tree.

I'll make a v2 if you want me to.

-- Steve