Re: [PATCH] function_graph: restore direct mode when callbacks drop to one

[Steven Rostedt]

On Fri, 13 Feb 2026 10:34:24 +0800 (CST)
<hu.shengming@xxxxxxxxxx> wrote:

> From: Shengming Hu <hu.shengming@xxxxxxxxxx>
> 
> When registering a second fgraph callback, direct path is disabled
> and array loop is used instead.
> When ftrace_graph_active falls back to one, we try to re-enable direct
> mode via ftrace_graph_enable_direct(true, ...).
> But ftrace_graph_enable_direct() incorrectly disables the static key
> rather than enabling it.
> This leaves fgraph_do_direct permanently off after first multi-callback
> transition, so direct fast mode is never restored.

Good catch!

> 
> Fixes: cc60ee813b503 ("function_graph: Use static_call and branch to optimize entry function")
> Signed-off-by: Shengming Hu <hu.shengming@xxxxxxxxxx>
> ---
> kernel/trace/fgraph.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index cc48d16be43e..4df766c690f9 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1303,7 +1303,7 @@ static void ftrace_graph_enable_direct(bool enable_branch, struct fgraph_ops *go
> static_call_update(fgraph_func, func);
> static_call_update(fgraph_retfunc, retfunc);
> if (enable_branch)
> -       static_branch_disable(&fgraph_do_direct);
> +       static_branch_enable(&fgraph_do_direct);
> }

Your email client killed your patch. it has huge white-space damage.
But because it's such a trivial change, I'll fix it up for you. But
next time please make sure your email client doesn't corrupt your
patches.

Thanks,

-- Steve


> 
> static void ftrace_graph_disable_direct(bool disable_branch)
> --
> 2.25.1