Re: [PATCH v5 bpf-next 2/4] ftrace: Allow IPMODIFY and DIRECT ops on the same function

From: Naveen N. Rao
Date: Fri Sep 09 2022 - 14:14:10 EST


Hi Song,

Song Liu wrote:


On Sep 9, 2022, at 4:58 AM, Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxx> wrote:

Song Liu wrote:

[...]

+
/**
* register_ftrace_function - register a function for profiling
* @ops: ops structure that holds the function for profiling.
@@ -8018,14 +8206,15 @@ int register_ftrace_function(struct ftrace_ops *ops)
{
int ret;
- ftrace_ops_init(ops);
-
- mutex_lock(&ftrace_lock);
-
- ret = ftrace_startup(ops, 0);
+ lock_direct_mutex();

Trying to enable ftrace direct on powerpc, this is resulting in a hung task when testing samples/ftrace/ftrace-direct-modify.c

Essentially, the sample calls modify_ftrace_direct(), which grabs direct_mutex before calling ftrace_modify_direct_caller()->register_ftrace_function().


Thanks for the report. Would the following change fix the issue?

Song

diff --git i/kernel/trace/ftrace.c w/kernel/trace/ftrace.c
index bc921a3f7ea8..2f1e6cfa834e 100644
--- i/kernel/trace/ftrace.c
+++ w/kernel/trace/ftrace.c
@@ -5496,7 +5496,7 @@ int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
if (ret)
goto out_lock;

- ret = register_ftrace_function(&stub_ops);
+ ret = register_ftrace_function_nolock(&stub_ops);
if (ret) {
ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
goto out_lock;


That fixes it for me.
Reported-and-Tested-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>


Thanks!
- Naveen