Re: [PATCH 1/8] ftrace: Replace uses of _ftrace_direct APIs with _ftrace_direct_multi

Mark Rutland
2023-02-02T15:03:23Z

On Wed, Feb 01, 2023 at 05:34:13PM +0100, Florent Revest wrote:
> The _multi API requires that users keep their own ops and can enforce
> that an op is only associated to one direct call.
>
> Signed-off-by: Florent Revest <revest@chromium.org>
> ---
> kernel/trace/trace_selftest.c | 9 ++++++---
> samples/ftrace/ftrace-direct-modify.c | 11 +++++++----
> samples/ftrace/ftrace-direct-too.c | 12 +++++++-----
> samples/ftrace/ftrace-direct.c | 12 +++++++-----

Looking at samples/ftrace/, as of this patch we have a few samples that are
almost identical, modulo the function being traced, and some different register
shuffling for arguments:

* ftrace-direct.c and ftrace-direct-multi.c
* ftrace-direct-modify.c and ftrace-direct-modify

... perhaps it would be better to just delete the !multi versions ?

Regardless, the changes below look functionally correct to me. I gave it a spin
on x86_64, both with the FTRACE_STARTUP_TEST, and loading the modules
dynamically, and those were all happy:

| # mount -t tracefs none /sys/kernel/tracing/
| # for KO in *.ko; do
| > echo $KO;
| > insmod $KO;
| > cat /sys/kernel/tracing/enabled_functions
| > rmmod $KO;
| > done
| ftrace-direct-modify.ko
| [ 91.890089]
| [ 91.890600] **********************************************************
| [ 91.892277] ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
| [ 91.893912] ** **
| [ 91.895569] ** trace_printk() being used. Allocating extra memory. **
| [ 91.897215] ** **
| [ 91.898861] ** This means that this is a DEBUG kernel and it is **
| [ 91.900517] ** unsafe for production use. **
| [ 91.902138] ** **
| [ 91.903755] ** If you see this message and you are not debugging **
| [ 91.905378] ** the kernel, report this immediately to your vendor! **
| [ 91.907010] ** **
| [ 91.908625] ** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **
| [ 91.910221] **********************************************************
| schedule (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp1+0x0/0x1d [ftrace_direct_modify]
| ftrace-direct-multi-modify.ko
| wake_up_process (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp1+0x0/0x23 [ftrace_direct_multi_modify]
| schedule (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp1+0x0/0x23 [ftrace_direct_multi_modify]
| ftrace-direct-multi.ko
| wake_up_process (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp+0x0/0x30 [ftrace_direct_multi]
| schedule (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp+0x0/0x30 [ftrace_direct_multi]
| ftrace-direct-too.ko
| handle_mm_fault (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp+0x0/0x30 [ftrace_direct_too]
| ftrace-direct.ko
| wake_up_process (1) R D tramp: ftrace_regs_caller+0x0/0x66 (call_direct_funcs+0x0/0x20)
| direct-->my_tramp+0x0/0x20 [ftrace_direct]

So FWIW:

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

Mark.

> 4 files changed, 27 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
> index ff0536cea968..9b7f10cbc51d 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 = {};
> +#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;
>
> @@ -891,7 +894,7 @@ trace_selftest_startup_function_graph(struct tracer *trace,
>
> unregister_ftrace_graph(&fgraph_ops);
>
> - ret = unregister_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
> + 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..e1e6c286970c 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 +131,8 @@ 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 +141,12 @@ 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);
> }
>
> 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);
> }
>
> 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);
> }
>
> 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");
> --
> 2.39.1.519.gcb327c4b5f-goog