Re: [PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

[Steven Rostedt]

On Mon,  6 Oct 2025 13:58:47 -0400
Sasha Levin <sas...@kernel.org> wrote:

> diff --git a/kernel/trace/trace_sched_wakeup.c 
> b/kernel/trace/trace_sched_wakeup.c
> index bf1cb80742aed..fa48bbdf0851c 100644
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -138,8 +138,11 @@ static int wakeup_graph_entry(struct ftrace_graph_ent 
> *trace,
>               return 0;
>  
>       calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
> -     if (!calltime)
> +     if (!calltime) {
> +             local_dec(&data->disabled);
> +             preempt_enable_notrace();
>               return 0;
> +     }
>  
>       *calltime = trace_clock_local();
>  
> @@ -169,8 +172,11 @@ static void wakeup_graph_return(struct ftrace_graph_ret 
> *trace,
>       rettime = trace_clock_local();
>  
>       calltime = fgraph_retrieve_data(gops->idx, &size);
> -     if (!calltime)
> +     if (!calltime) {
> +             local_dec(&data->disabled);
> +             preempt_enable_notrace();
>               return;
> +     }
>  
>       __trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
>       local_dec(&data->disabled);

Technically correct, but this would look better:

diff --git a/kernel/trace/trace_sched_wakeup.c 
b/kernel/trace/trace_sched_wakeup.c
index bf1cb80742ae..e3f2e4f56faa 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -138,12 +138,10 @@ static int wakeup_graph_entry(struct ftrace_graph_ent 
*trace,
                return 0;
 
        calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-       if (!calltime)
-               return 0;
-
-       *calltime = trace_clock_local();
-
-       ret = __trace_graph_entry(tr, trace, trace_ctx);
+       if (calltime) {
+               *calltime = trace_clock_local();
+               ret = __trace_graph_entry(tr, trace, trace_ctx);
+       }
        local_dec(&data->disabled);
        preempt_enable_notrace();
 
@@ -169,12 +167,10 @@ static void wakeup_graph_return(struct ftrace_graph_ret 
*trace,
        rettime = trace_clock_local();
 
        calltime = fgraph_retrieve_data(gops->idx, &size);
-       if (!calltime)
-               return;
+       if (calltime)
+               __trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 
-       __trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
        local_dec(&data->disabled);
-
        preempt_enable_notrace();
        return;
 }


-- Steve