Re: [PATCH bpf-next v2] selftests/bpf: port test_ftrace.sh to test_progs

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Nov 04, 2026 at 10:59:33AM +0100, Alexis Lothoré (eBPF Foundation) wrote:
> Commit ff205766dbbe ("ftrace: Fix function_graph tracer interaction with
> BPF trampoline") made sure that trampolines generated for tracing
> programs did not collide with the function graph when we are returning
> from the hooked function. The series bringing this commit also came with
> a new test ensuring that the kernel does not crash when executing BPF
> programs handled by trampolines while the function graph trace is
> enabled, but this test is a standalone shell script, hence not executed
> in CI.
> 
> Convert the script to the test_progs runner so it can be executed
> automatically by the CI infrastructure. There are two main options to
> port this test:
>   - just enable ftrace during some existing trampoline-related tests
>     (eg: fentry/fexit tests)
>   - create a dedicated, minimal test with function graph
> 
> The new test adopts the latter approach, with a smaller scope to keep
> execution time reasonable, while reusing an existing
> fentry/fexit/fmod_ret test. Despite the few asserts in the new test, the
> actual goal is to make sure that the kernel does not crash because of
> some incorrect stack frame skipping when both the function graph and
> tracing programs are running.
> 
> ftrace is configured through a dedicated ftrace instance which is
> dropped at the end of the test.
> 
> With the new test integrated into test_progs, drop test_ftrace.sh.
> 
> Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
> ---
> Hello,
> this is v2 of a small series aiming to port the test_ftrace.sh script
> (testing that trampolines and function graph behave correctly when both
> are enabled) into the test_progs framework. The test is heavily
> simplified following Alexei's review and suggestions.
> ---
> Changes in v2:
> - use a ftrace instance rather than global ftrace
> - drop fgraph filters
> - drop custom ftrace helpers in favor of direct manipulation in test
> - drop custom bpf prog, reuse test_modify_return directly
> - move test in existing test file (modify_return.c)
> - make the test parallel (drop serial_)
> - Link to v1: https://patch.msgid.link/20261030-ftrace_in_test_progs-v1-0-aa50c5dd1ccc@bootlin.com

lgtm, it might be worth to add something like this also for
tracing-multi (maybe also kprobe-multi) and run some tests
with function or function_graph enabled

Reviewed-by: Jiri Olsa <jolsa@kernel.org>

jirka

SNIP

> +void test_modify_return_graph(void)
> +{
> +	char instance[MAX_INSTANCE_PATH_LEN];
> +	char *ftrace_dir;
> +	int ret;
> +
> +	ftrace_dir = access(TRACE_FTRACE_DEFAULT, F_OK) ? TRACEFS_IN_DEBUGFS :
> +							  TRACEFS_DEFAULT;
> +
> +	ret = snprintf(instance, MAX_INSTANCE_PATH_LEN,
> +		       "%s/instances/bpf-XXXXXX", ftrace_dir);
> +	if (ret < 0)
> +		return;
> +
> +	if (!ASSERT_OK_PTR(mkdtemp(instance), "mkdtemp"))
> +		return;
> +
> +	SYS(out, "echo 'bpf_modify_return_test*' > %s/set_ftrace_filter",
> +	    instance);

nit, no need for new line

> +	SYS(out, "echo function_graph > %s/current_tracer", instance);
> +
> +	test_modify_return();
> +
> +	SYS(out, "grep -q bpf_modify_return_test2 %s/trace", instance);
> +out:
> +	ASSERT_OK(rmdir(instance), "rmdir");
> +}
> diff --git a/tools/testing/selftests/bpf/test_ftrace.sh b/tools/testing/selftests/bpf/test_ftrace.sh
> deleted file mode 100755
> index f5109eb0e951..000000000000
> --- a/tools/testing/selftests/bpf/test_ftrace.sh
> +++ /dev/null
> @@ -1,44 +0,0 @@
> -#!/bin/bash
> -
> -if [[ -e /sys/kernel/tracing/trace ]]; then
> -    TR=/sys/kernel/tracing/
> -else
> -    TR=/sys/kernel/debug/tracing/
> -fi
> -
> -clear_trace() { # reset trace output
> -    echo > $TR/trace
> -}
> -
> -disable_tracing() { # stop trace recording
> -    echo 0 > $TR/tracing_on
> -}
> -
> -enable_tracing() { # start trace recording
> -    echo 1 > $TR/tracing_on
> -}
> -
> -reset_tracer() { # reset the current tracer
> -    echo nop > $TR/current_tracer
> -}
> -
> -disable_tracing
> -clear_trace
> -
> -echo "" > $TR/set_ftrace_filter
> -echo '*printk* *console* *wake* *serial* *lock*' > $TR/set_ftrace_notrace
> -
> -echo "bpf_prog_test*" > $TR/set_graph_function
> -echo "" > $TR/set_graph_notrace
> -
> -echo function_graph > $TR/current_tracer
> -
> -enable_tracing
> -./test_progs -t fentry
> -./test_progs -t fexit
> -disable_tracing
> -clear_trace
> -
> -reset_tracer
> -
> -exit 0
> 
> ---
> base-commit: b0e67f50519538b1b4c6364edc7811f482703f75
> change-id: 20261027-ftrace_in_test_progs-d5f70a2330ac
> 
> Best regards,
> --  
> Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>
>