linux-kernel - Re: [PATCH] ftrace: Show a list of all functions that have ever been enabled

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Date:   Wed, 25 Jan 2023 09:29:31 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>, chriscli@...gle.com
Subject: Re: [PATCH] ftrace: Show a list of all functions that have ever been
 enabled

On Tue, Jan 24, 2023 at 02:06:17PM -0500, Steven Rostedt wrote:
> On Tue, 24 Jan 2023 16:27:23 +0000
> Mark Rutland <mark.rutland@....com> wrote:
> 
> > > [
> > >   This patch will conflict with Mark's patch that is going through the ARM
> > >   tree. I will hold off pulling this patch until the next merge window, and
> > >   rebase it on top of the changes when the tracing tree merges with upstream
> > >   that has the changes from the ARM tree.
> > > ]  
> > 
> > Sorry for the conflict!
> 
> No problem. This was more to help us debug something, and we are currently
> just backporting it for now to our kernels in order to help with the
> crashes we are seeing. No rush to get it upstream. But I figured that if it
> can help us, it can also help others.

Indeed!

> > The patch looks good to me; I just gave it a spin on arm64 (resolving the
> > conflcit with my changes by moving FTRCE_FL_TOUCHED to bit 20, and
> > FTRACE_REF_MAX_SHIFT down to 20), and from a naive test that seems happy:
> > 
> > | # cat /sys/kernel/tracing/touched_functions 
> > | # echo do_el0_svc > /sys/kernel/tracing/set_ftrace_filter 
> > | # echo function_graph > /sys/kernel/tracing/current_tracer 
> > | # cat /sys/kernel/tracing/touched_functions 
> > | do_el0_svc (1)       O  ops: graph_ops+0x0/0xb8 (ftrace_graph_func+0x0/0x58)
> > | # echo nop > /sys/kernel/tracing/current_tracer 
> > | # cat /sys/kernel/tracing/touched_functions 
> > | do_el0_svc (0) 
> 
> Thanks for testing! I guess I can add a "tested-by" from you?

Yes, please feel free to add:

Tested-by: Mark Rutland <mark.rutland@....com>

... and I'm happy to test the rebased version once this marge window as
settled.

Thanks,
Mark.