Messages in this thread | | | From | Song Shuai <> | Date | Wed, 23 Nov 2022 01:58:18 +0000 | Subject | Re: [PATCH] ftrace: avoid replacing the list func with itself |
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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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