Re: [PATCH v4 1/2] ftrace: cleanup ftrace_graph_caller enable and disable

Mark Rutland
2022-04-19T12:54:11Z

On Sat, Apr 09, 2022 at 11:35:53PM +0800, Chengming Zhou wrote:
> The ftrace_[enable,disable]_ftrace_graph_caller() are used to do
> special hooks for graph tracer, which are not needed on some ARCHs
> that use graph_ops:func function to install return_hooker.
>
> So introduce the weak version in ftrace core code to cleanup
> in x86.
>
> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
> ---
> v4:
> - put weak ftrace_enable,disable_ftrace_graph_caller() in
> fgraph.c instead of ftrace.c as suggested by Steve.
>
> v3:
> - consolidate two #if into a single #if, suggested by Steve. Thanks.
> ---
> arch/x86/kernel/ftrace.c | 17 ++---------------
> kernel/trace/fgraph.c | 18 ++++++++++++++++++
> 2 files changed, 20 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
> index 1e31c7d21597..b09d73c2ba89 100644
> --- a/arch/x86/kernel/ftrace.c
> +++ b/arch/x86/kernel/ftrace.c
> @@ -579,9 +579,7 @@ void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
>
> #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>
> -#ifdef CONFIG_DYNAMIC_FTRACE
> -
> -#ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
> +#if defined(CONFIG_DYNAMIC_FTRACE) && !defined(CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS)
> extern void ftrace_graph_call(void);
> static const char *ftrace_jmp_replace(unsigned long ip, unsigned long addr)
> {
> @@ -610,18 +608,7 @@ int ftrace_disable_ftrace_graph_caller(void)
>
> return ftrace_mod_jmp(ip, &ftrace_stub);
> }
> -#else /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
> -int ftrace_enable_ftrace_graph_caller(void)
> -{
> - return 0;
> -}
> -
> -int ftrace_disable_ftrace_graph_caller(void)
> -{
> - return 0;
> -}
> -#endif /* CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
> -#endif /* !CONFIG_DYNAMIC_FTRACE */
> +#endif /* CONFIG_DYNAMIC_FTRACE && !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
>
> /*
> * Hook the return address and push it in the stack of return addrs
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 8f4fb328133a..289311680c29 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -30,6 +30,24 @@ int ftrace_graph_active;
> /* Both enabled by default (can be cleared by function_graph tracer flags */
> static bool fgraph_sleep_time = true;
>
> +/*
> + * archs can override this function if they must do something
> + * to enable hook for graph tracer.
> + */
> +int __weak ftrace_enable_ftrace_graph_caller(void)
> +{
> + return 0;
> +}
> +
> +/*
> + * archs can override this function if they must do something
> + * to disable hook for graph tracer.
> + */
> +int __weak ftrace_disable_ftrace_graph_caller(void)
> +{
> + return 0;
> +}

IIUC an arch should either:

* Have ftrace_graph_call()

* Have both ftrace_enable_ftrace_graph_caller() and
ftrace_disable_ftrace_graph_caller()

... and I can't think of a reason an arch would need both ftrace_graph_call()
*and* the enable/disable functions.

Given that, could we drop the `__weak` and place these within ifdeffery, i.e.
make the above:

| #ifndef ftrace_graph_call
| int ftrace_enable_ftrace_graph_caller(void) { return 0; }
| int ftrace_disable_ftrace_graph_caller(void) { return 0; }
| #endif /* ftrace_graph_call *.

That way we'd catch cases when:

* An architecture meant to provide one of these functions, but forgot (e.g. the
name got typo'd)

* An architecture provides an unnecessary implementation of either of these
functions.

Regardless, this looks ok to me. Steve, are you happy with this? I suspect we'd
need to take this via the arm64 tree with the next patch, so we'd need your Ack.

Thanks,
Mark.

> +
> /**
> * ftrace_graph_stop - set to permanently disable function graph tracing
> *
> --
> 2.35.1