Re: [PATCH 1/2] fgraph: fix thresh_return clear per-task notrace

[Google]

On Sat, 21 Feb 2026 11:30:07 +0800 (CST)
<hu.shengming@xxxxxxxxxx> wrote:

> From: Shengming Hu <hu.shengming@xxxxxxxxxx>
> 
> When tracing_thresh is enabled, function graph tracing uses
> trace_graph_thresh_return() as the return handler. Unlike
> trace_graph_return(), it did not clear the per-task
> TRACE_GRAPH_NOTRACE flag set by the entry handler for
> set_graph_notrace addresses. This could leave the task
> permanently in "notrace" state and effectively disable
> function graph tracing for that task.
> 
> Mirror trace_graph_return()'s per-task notrace handling by
> clearing TRACE_GRAPH_NOTRACE and returning early when set.
> 

Good catch!

Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>

Thanks!


> Fixes: b84214890a9bc ("function_graph: Move graph notrace bit to
> shadow stack global var")
> Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
> ---
>  kernel/trace/trace_functions_graph.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
> index 1de6f1573..cbe43680c 100644
> --- a/kernel/trace/trace_functions_graph.c
> +++ b/kernel/trace/trace_functions_graph.c
> @@ -400,14 +400,15 @@ static void trace_graph_thresh_return(struct ftrace_graph_ret *trace,
>  				      struct fgraph_ops *gops,
>  				      struct ftrace_regs *fregs)
>  {
> +	unsigned long *task_var = fgraph_get_task_var(gops);
>  	struct fgraph_times *ftimes;
>  	struct trace_array *tr;
>  	int size;
> 
>  	ftrace_graph_addr_finish(gops, trace);
> 
> -	if (trace_recursion_test(TRACE_GRAPH_NOTRACE_BIT)) {
> -		trace_recursion_clear(TRACE_GRAPH_NOTRACE_BIT);
> +	if (*task_var & TRACE_GRAPH_NOTRACE) {
> +		*task_var &= ~TRACE_GRAPH_NOTRACE;
>  		return;
>  	}
> 
> -- 
> 2.25.1


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>