Re: [PATCH] tracing: Reset the function filter after completing trampoline/graph selftest

From: Li Huafei
Date: Tue Apr 26 2022 - 04:01:10 EST

Hi Steve,

On 2022/4/26 6:58, Steven Rostedt wrote:
On Mon, 18 Apr 2022 15:39:58 +0800
Li Huafei <lihuafei1@xxxxxxxxxx> wrote:

The direct trampoline and graph coexistence test sets global_ops to
trace only 'trace_selftest_dynamic_test_func', but does not reset it
after the test is completed, resulting in the function filter being set
already after the system starts. Although it can be reset through the
tracefs interface, it is more or less confusing to the user, and we
should reset it to trace all functions after the trampoline/graph test

Fixes: 130c08065848 ("tracing: Add trampoline/graph selftest")
Signed-off-by: Li Huafei <lihuafei1@xxxxxxxxxx>
kernel/trace/trace_selftest.c | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index abcadbe933bb..e89f72571f8e 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -866,12 +866,12 @@ trace_selftest_startup_function_graph(struct tracer *trace,
ret = register_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
(unsigned long) trace_direct_tramp);
if (ret)
- goto out;
+ goto reset_filter;
ret = register_ftrace_graph(&fgraph_ops);
if (ret) {
warn_failed_init_tracer(trace, ret);
- goto out;
+ goto reset_filter;
@@ -887,14 +887,18 @@ trace_selftest_startup_function_graph(struct tracer *trace,
ret = unregister_ftrace_direct((unsigned long) DYN_FTRACE_TEST_NAME,
(unsigned long) trace_direct_tramp);
if (ret)
- goto out;
+ goto reset_filter;
if (!ret && !count) {
ret = -1;
- goto out;
+ goto reset_filter;
No need for all the 'goto reset_filter', if this function fails, then the
tracer is disabled, and there's no reason to clear the filter. In fact, it
Thank you for the review. I see that we will disable function_graph tracer:

     /* Stop it if we failed */
     if (ret)

But there is no function tracer disabled. Am I missing something that would disable the function tracer?

may cause a crash (because something bad happened).

Yes, so should we kill ftrace when the function_graph test fails?


-- Steve

+ /* Enable tracing on all functions again */
+ ftrace_set_global_filter(NULL, 0, 1);
/* Don't test dynamic tracing, the function tracer already did */