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SubjectRe: [PATCH] ftrace: Avoid needless updates of the ftrace function call
On Wed, 23 Nov 2022 10:29:28 +0800
Song Shuai <suagrfillet@gmail.com> wrote:

> > @@ -2783,7 +2796,7 @@ void ftrace_modify_all_code(int command)
> > * traced.
> > */
> > if (update) {
> > - err = ftrace_update_ftrace_func(ftrace_ops_list_func);
> > + err = update_ftrace_func(ftrace_ops_list_func);
> > if (FTRACE_WARN_ON(err))
> > return;
> > }
> > @@ -2799,7 +2812,7 @@ void ftrace_modify_all_code(int command)
> > /* If irqs are disabled, we are in stop machine */
> > if (!irqs_disabled())
> > smp_call_function(ftrace_sync_ipi, NULL, 1);
> > - err = ftrace_update_ftrace_func(ftrace_trace_function);
> > + err = update_ftrace_func(ftrace_trace_function);
> The helper function should only serve the ftrace_ops_list_func.
>
> And ftrace_trace_function is always different in this function with
> FTRACE_UPDATE_TRACE_FUNC command.
>
> So this place should be left as it is.

But it is needed to update the static variable. Without this change,
then save_func will get set to ftrace_ops_list_func and never change
after that and then the update to ftrace_ops_list_func will stop happening.

-- Steve

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