[PATCH] tracing/osnoise: Use built-in RCU list checking

[PATCH] tracing/osnoise: Use built-in RCU list checking

[Chuang Wang]

list_for_each_entry_rcu() has built-in RCU and lock checking.

Pass cond argument to list_for_each_entry_rcu() to silence false lockdep
warning when CONFIG_PROVE_RCU_LIST is enabled.

Execute as follow:

 [tracing]# echo osnoise > current_tracer
 [tracing]# echo 1 > tracing_on
 [tracing]# echo 0 > tracing_on

The trace_types_lock is held when osnoise_tracer_stop() or
timerlat_tracer_stop() are called in the non-RCU read side section.
So, pass lockdep_is_held(&trace_types_lock) to silence false lockdep
warning.

Fixes: dae181349f1e ("tracing/osnoise: Support a list of trace_array *tr")
Signed-off-by: Chuang Wang <nashuiliang@gmail.com>
---
 kernel/trace/trace_osnoise.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index 94c1b5eb1dc0..210e1f168392 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -147,9 +147,8 @@ static void osnoise_unregister_instance(struct trace_array *tr)
 	 * register/unregister serialization is provided by trace's
 	 * trace_types_lock.
 	 */
-	lockdep_assert_held(&trace_types_lock);
-
-	list_for_each_entry_rcu(inst, &osnoise_instances, list) {
+	list_for_each_entry_rcu(inst, &osnoise_instances, list,
+				lockdep_is_held(&trace_types_lock)) {
 		if (inst->tr == tr) {
 			list_del_rcu(&inst->list);
 			found = 1;
-- 
2.37.2

Re: [PATCH] tracing/osnoise: Use built-in RCU list checking

[Daniel Bristot de Oliveira]

On 12/27/22 03:30, Chuang Wang wrote:
> list_for_each_entry_rcu() has built-in RCU and lock checking.
> 
> Pass cond argument to list_for_each_entry_rcu() to silence false lockdep
> warning when CONFIG_PROVE_RCU_LIST is enabled.
> 
> Execute as follow:
> 
>  [tracing]# echo osnoise > current_tracer
>  [tracing]# echo 1 > tracing_on
>  [tracing]# echo 0 > tracing_on
> 
> The trace_types_lock is held when osnoise_tracer_stop() or
> timerlat_tracer_stop() are called in the non-RCU read side section.
> So, pass lockdep_is_held(&trace_types_lock) to silence false lockdep
> warning.
> 
> Fixes: dae181349f1e ("tracing/osnoise: Support a list of trace_array *tr")
> Signed-off-by: Chuang Wang <nashuiliang@gmail.com>

Acked-by: Daniel Bristot de Oliveira <bristot@kernel.org>

Thanks!
-- Daniel