[PATCH] ftrace: Avoid needless updates of the ftrace function call
From: Steven Rostedt <rostedt@goodmis.org>
Date: 2022-11-22 23:09:21
Also in:
lkml
Subsystem:
function hooks (ftrace), the rest, tracing · Maintainers:
Steven Rostedt, Masami Hiramatsu, Linus Torvalds
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/ (local)
Reported-by: Song Shuai <redacted>
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