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Message-ID: <CABRcYmKeYM9cG2=ZLTmVL3PA+zqzBd_NUP059tochsus0-9Rnw@mail.gmail.com>
Date: Thu, 16 Mar 2023 16:40:38 +0100
From: Florent Revest <revest@...omium.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org,
catalin.marinas@....com, will@...nel.org, mhiramat@...nel.org,
mark.rutland@....com, ast@...nel.org, daniel@...earbox.net,
andrii@...nel.org, kpsingh@...nel.org, jolsa@...nel.org,
xukuohai@...weicloud.com, lihuafei1@...wei.com
Subject: Re: [PATCH v2 01/10] ftrace: Replace uses of _ftrace_direct APIs with _ftrace_direct_multi
On Thu, Mar 16, 2023 at 12:33 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Tue, 7 Feb 2023 19:21:26 +0100
> Florent Revest <revest@...omium.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@...omium.org>
> > Acked-by: Mark Rutland <mark.rutland@....com>
> > Tested-by: Mark Rutland <mark.rutland@....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.
Agreed.
> > +#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.
Ah yes, good catch.
>
> >
> > @@ -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.
I agree, it's otherwise quite easy to miss the ftrace_free_filter. :)
I'll add a patch introducing this "free_filters" arg in the new subset
series that I'll send you directly.
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