| Message ID | 20221122180905.737b6f52@gandalf.local.home (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | bd604f3db49c5b21171abea0414a2020dcbf2646 |
| Headers | show |
| Series | ftrace: Avoid needless updates of the ftrace function call | expand |
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
Steven Rostedt <rostedt@goodmis.org> 于2022年11月23日周三 03:17写道： > > 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 Yes, you're right. Thx for your explanation. -- Song
On Tue, 22 Nov 2022 18:09:05 -0500 Steven Rostedt <rostedt@goodmis.org> wrote: > From: "Steven Rostedt (Google)" <rostedt@goodmis.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@kernel.org> Thank you, > Reported-by: Song Shuai <suagrfillet@gmail.com> > Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.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 >
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; }