Messages in this thread Patch in this message | | | Date | Tue, 22 Nov 2022 16:32:25 -0500 | From | Steven Rostedt <> | Subject | Re: [PATCH] ftrace: avoid replacing the list func with itself |
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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
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; }
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