Re: [PATCH v2 01/10] ftrace: Replace uses of _ftrace_direct APIs with _ftrace_direct_multi

From: Steven Rostedt <rostedt@goodmis.org>
To: Florent Revest <revest@chromium.org>
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
	bpf@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org,
	mhiramat@kernel.org, mark.rutland@arm.com, ast@kernel.org,
	daniel@iogearbox.net, andrii@kernel.org, kpsingh@kernel.org,
	jolsa@kernel.org, xukuohai@huaweicloud.com, lihuafei1@huawei.com
Subject: Re: [PATCH v2 01/10] ftrace: Replace uses of _ftrace_direct APIs with _ftrace_direct_multi
Date: Wed, 15 Mar 2023 19:33:55 -0400	[thread overview]
Message-ID: <20230315193355.30c48764@gandalf.local.home> (raw)
In-Reply-To: <20230207182135.2671106-2-revest@chromium.org>

On Tue,  7 Feb 2023 19:21:26 +0100
Florent Revest <revest@chromium.org> wrote:

> The _multi API requires that users keep their own ops but can enforce
> that an op is only associated to one direct call.
> 
> Signed-off-by: Florent Revest <revest@chromium.org>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Mark Rutland <mark.rutland@arm.com>
> ---
>  kernel/trace/trace_selftest.c         | 11 +++++++----
>  samples/ftrace/ftrace-direct-modify.c | 12 ++++++++----
>  samples/ftrace/ftrace-direct-too.c    | 12 +++++++-----
>  samples/ftrace/ftrace-direct.c        | 12 +++++++-----
>  4 files changed, 29 insertions(+), 18 deletions(-)
> 
> diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
> index ff0536cea968..57221f69a33b 100644
> --- a/kernel/trace/trace_selftest.c
> +++ b/kernel/trace/trace_selftest.c
> @@ -806,6 +806,9 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>  	int ret;
>  	unsigned long count;
>  	char *func_name __maybe_unused;
> +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> +	struct ftrace_ops direct = {};

Make this static to the file and move it above to where there's already an
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS block.

Less #ifdef is better, and also, I don't like having as an example an
ftrace_ops structure allocated on the stack. It can become increasingly
larger as time goes by. I don't want to encourage placing it on stacks.

> +#endif
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE
>  	if (ftrace_filter_param) {
> @@ -870,8 +873,8 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>  	 * Register direct function together with graph tracer
>  	 * and make sure we get graph trace.
>  	 */
> -	ret = register_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
> -				     (unsigned long) trace_direct_tramp);
> +	ftrace_set_filter_ip(&direct, (unsigned long)DYN_FTRACE_TEST_NAME, 0, 0);
> +	ret = register_ftrace_direct_multi(&direct, (unsigned long)trace_direct_tramp);
>  	if (ret)
>  		goto out;

I had to rebase this code on top of the latest tree because of updates.
Which is good, because this patch requires those same. When using
ftrace_set_filter_ip() one needs to call

   ftrace_free_filter(&direct);

Because the ftrace_set_filter_ip() allocates hashs on the ftrace_ops and
those need to be freed.

>  
> @@ -891,8 +894,8 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>  
>  	unregister_ftrace_graph(&fgraph_ops);
>  
> -	ret = unregister_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
> -				       (unsigned long) trace_direct_tramp);
> +	ret = unregister_ftrace_direct_multi(&direct,
> +					     (unsigned long) trace_direct_tramp);
>  	if (ret)
>  		goto out;
>  
> diff --git a/samples/ftrace/ftrace-direct-modify.c b/samples/ftrace/ftrace-direct-modify.c
> index de5a0f67f320..ecd76f75cb80 100644
> --- a/samples/ftrace/ftrace-direct-modify.c
> +++ b/samples/ftrace/ftrace-direct-modify.c
> @@ -96,6 +96,8 @@ asm (
>  
>  #endif /* CONFIG_S390 */
>  
> +static struct ftrace_ops direct;
> +
>  static unsigned long my_tramp = (unsigned long)my_tramp1;
>  static unsigned long tramps[2] = {
>  	(unsigned long)my_tramp1,
> @@ -114,7 +116,7 @@ static int simple_thread(void *arg)
>  		if (ret)
>  			continue;
>  		t ^= 1;
> -		ret = modify_ftrace_direct(my_ip, my_tramp, tramps[t]);
> +		ret = modify_ftrace_direct_multi(&direct, tramps[t]);
>  		if (!ret)
>  			my_tramp = tramps[t];
>  		WARN_ON_ONCE(ret);
> @@ -129,7 +131,9 @@ static int __init ftrace_direct_init(void)
>  {
>  	int ret;
>  
> -	ret = register_ftrace_direct(my_ip, my_tramp);
> +	ftrace_set_filter_ip(&direct, (unsigned long) my_ip, 0, 0);
> +	ret = register_ftrace_direct_multi(&direct, my_tramp);
> +
>  	if (!ret)
>  		simple_tsk = kthread_run(simple_thread, NULL, "event-sample-fn");
>  	return ret;
> @@ -138,12 +142,12 @@ static int __init ftrace_direct_init(void)
>  static void __exit ftrace_direct_exit(void)
>  {
>  	kthread_stop(simple_tsk);
> -	unregister_ftrace_direct(my_ip, my_tramp);
> +	unregister_ftrace_direct_multi(&direct, my_tramp);

Same here.

>  }
>  
>  module_init(ftrace_direct_init);
>  module_exit(ftrace_direct_exit);
>  
>  MODULE_AUTHOR("Steven Rostedt");
> -MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct()");
> +MODULE_DESCRIPTION("Example use case of using modify_ftrace_direct_multi()");
>  MODULE_LICENSE("GPL");
> diff --git a/samples/ftrace/ftrace-direct-too.c b/samples/ftrace/ftrace-direct-too.c
> index e13fb59a2b47..0e907092e2c0 100644
> --- a/samples/ftrace/ftrace-direct-too.c
> +++ b/samples/ftrace/ftrace-direct-too.c
> @@ -70,21 +70,23 @@ asm (
>  
>  #endif /* CONFIG_S390 */
>  
> +static struct ftrace_ops direct;
> +
>  static int __init ftrace_direct_init(void)
>  {
> -	return register_ftrace_direct((unsigned long)handle_mm_fault,
> -				     (unsigned long)my_tramp);
> +	ftrace_set_filter_ip(&direct, (unsigned long) handle_mm_fault, 0, 0);
> +
> +	return register_ftrace_direct_multi(&direct, (unsigned long) my_tramp);
>  }
>  
>  static void __exit ftrace_direct_exit(void)
>  {
> -	unregister_ftrace_direct((unsigned long)handle_mm_fault,
> -				 (unsigned long)my_tramp);
> +	unregister_ftrace_direct_multi(&direct, (unsigned long)my_tramp);

And here.

>  }
>  
>  module_init(ftrace_direct_init);
>  module_exit(ftrace_direct_exit);
>  
>  MODULE_AUTHOR("Steven Rostedt");
> -MODULE_DESCRIPTION("Another example use case of using register_ftrace_direct()");
> +MODULE_DESCRIPTION("Another example use case of using register_ftrace_direct_multi()");
>  MODULE_LICENSE("GPL");
> diff --git a/samples/ftrace/ftrace-direct.c b/samples/ftrace/ftrace-direct.c
> index 1f769d0db20f..e446c38f6b58 100644
> --- a/samples/ftrace/ftrace-direct.c
> +++ b/samples/ftrace/ftrace-direct.c
> @@ -63,21 +63,23 @@ asm (
>  
>  #endif /* CONFIG_S390 */
>  
> +static struct ftrace_ops direct;
> +
>  static int __init ftrace_direct_init(void)
>  {
> -	return register_ftrace_direct((unsigned long)wake_up_process,
> -				     (unsigned long)my_tramp);
> +	ftrace_set_filter_ip(&direct, (unsigned long) wake_up_process, 0, 0);
> +
> +	return register_ftrace_direct_multi(&direct, (unsigned long) my_tramp);
>  }
>  
>  static void __exit ftrace_direct_exit(void)
>  {
> -	unregister_ftrace_direct((unsigned long)wake_up_process,
> -				 (unsigned long)my_tramp);
> +	unregister_ftrace_direct_multi(&direct, (unsigned long)my_tramp);

And here.

Maybe we could add a parameter to unregister_ftrace_direct_multi():

  bool free_filters

when set, it will call the ftrace_free_filter(), as it looks like there's a
common code path here:

	ftrace_set_filter_ip();
	register_ftrace_direct_multi();
	[..]
	unregister_ftrace_direct_multi();
	ftrace_free_filter();

Add the option will save people from having to do that last step, and also
remind people that the filters need to be freed.

-- Steve

>  }
>  
>  module_init(ftrace_direct_init);
>  module_exit(ftrace_direct_exit);
>  
>  MODULE_AUTHOR("Steven Rostedt");
> -MODULE_DESCRIPTION("Example use case of using register_ftrace_direct()");
> +MODULE_DESCRIPTION("Example use case of using register_ftrace_direct_multi()");
>  MODULE_LICENSE("GPL");

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