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SubjectRe: [PATCH] ftrace: avoid replacing the list func with itself
Steven Rostedt <rostedt@goodmis.org> 于2022年11月22日周二 21:32写道:
>
> On Tue, 22 Nov 2022 02:28:25 +0000
> Song Shuai <suagrfillet@gmail.com> wrote:
>
> > Song Shuai <suagrfillet@gmail.com> 于2022年10月26日周三 13:20写道:
> > >
> > > The list func (ftrace_ops_list_func) will be patched first
> > > before the transition between old and new calls are set,
> > > which fixed the race described in this commit `59338f75`.
> > >
> > > While ftrace_trace_function changes from the list func to a
> > > ftrace_ops func, like unregistering the klp_ops to leave the only
> > > global_ops in ftrace_ops_list, the ftrace_[regs]_call will be
> > > replaced with the list func although it already exists. So there
> > > should be a condition to avoid this.
> > >
> > > This patch backups saved_ftrace_func by saved_ftrace_func_old
> > > which will be compared with the list func before trying to patch it.
> > >
> > Ping...
>
> Wouldn't something like this be simpler and easier to manage (without
> adding another variable to keep track of)?
>
> -- Steve
>
Thanks for the corrections, this looks great to me.
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 65a5d36463e0..d04552c0c275 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2763,6 +2763,19 @@ void __weak ftrace_arch_code_modify_post_process(void)
> {
> }
>
> +static int update_ftrace_func(ftrace_func_t func)
> +{
> + static ftrace_func_t save_func;
> +
> + /* Avoid updating if it hasn't changed */
> + if (func == save_func)
> + return 0;
> +
> + save_func = func;
> +
> + return ftrace_update_ftrace_func(func);
> +}
> +
> void ftrace_modify_all_code(int command)
> {
> int update = command & FTRACE_UPDATE_TRACE_FUNC;
> @@ -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);
> if (FTRACE_WARN_ON(err))
> return;
> }
Thanks,
Song

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