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Message-Id: <20221124003047.827b6ef942b0dc529face3b9@kernel.org> Date: Thu, 24 Nov 2022 00:30:47 +0900 From: Masami Hiramatsu (Google) <mhiramat@...nel.org> To: Steven Rostedt <rostedt@...dmis.org> Cc: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel <linux-trace-kernel@...r.kernel.org>, Masami Hiramatsu <mhiramat@...nel.org>, Song Shuai <suagrfillet@...il.com> Subject: Re: [PATCH] ftrace: Avoid needless updates of the ftrace function call On Tue, 22 Nov 2022 18:09:05 -0500 Steven Rostedt <rostedt@...dmis.org> wrote: > From: "Steven Rostedt (Google)" <rostedt@...dmis.org> > > Song Shuai reported: > > 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. > > And suggested using another variable to keep track of what the ftrace > function is set to. But this could be simplified by using a helper > function that does the same with a static variable. > > Link: https://lore.kernel.org/lkml/20221026132039.2236233-1-suagrfillet@gmail.com/ > This looks good to me. Reviewed-by: Masami Hiramatsu (Google) <mhiramat@...nel.org> Thank you, > Reported-by: Song Shuai <suagrfillet@...il.com> > Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org> > --- > kernel/trace/ftrace.c | 17 +++++++++++++++-- > 1 file changed, 15 insertions(+), 2 deletions(-) > > 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; > } > -- > 2.35.1 > -- Masami Hiramatsu (Google) <mhiramat@...nel.org>
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