Introduce CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING config option to control whether ftrace low-level code performs additional rcu_is_watching()-based validation logic in an attempt to catch noinstr violations. This check is expected to never be true and is mostly useful for low-level validation of ftrace subsystem invariants. For most users it should probably be kept disabled to eliminate unnecessary runtime overhead. This improves BPF multi-kretprobe (relying on ftrace and rethook infrastructure) runtime throughput by 2%, according to BPF benchmarks ([0]). [0] https://lore.kernel.org/bpf/CAEf4BzauQ2WKMjZdc9s0rBWa01BYbgwHN6aNDXQSHYia47pQ-w@xxxxxxxxxxxxxx/ Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx> Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx> --- include/linux/trace_recursion.h | 2 +- kernel/trace/Kconfig | 13 +++++++++++++ 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h index d48cd92d2364..24ea8ac049b4 100644 --- a/include/linux/trace_recursion.h +++ b/include/linux/trace_recursion.h @@ -135,7 +135,7 @@ extern void ftrace_record_recursion(unsigned long ip, unsigned long parent_ip); # define do_ftrace_record_recursion(ip, pip) do { } while (0) #endif -#ifdef CONFIG_ARCH_WANTS_NO_INSTR +#ifdef CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING # define trace_warn_on_no_rcu(ip) \ ({ \ bool __ret = !rcu_is_watching(); \ diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig index 61c541c36596..7aebd1b8f93e 100644 --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -974,6 +974,19 @@ config FTRACE_RECORD_RECURSION_SIZE This file can be reset, but the limit can not change in size at runtime. +config FTRACE_VALIDATE_RCU_IS_WATCHING + bool "Validate RCU is on during ftrace execution" + depends on FUNCTION_TRACER + depends on ARCH_WANTS_NO_INSTR + help + All callbacks that attach to the function tracing have some sort of + protection against recursion. This option is only to verify that + ftrace (and other users of ftrace_test_recursion_trylock()) are not + called outside of RCU, as if they are, it can cause a race. But it + also has a noticeable overhead when enabled. + + If unsure, say N + config RING_BUFFER_RECORD_RECURSION bool "Record functions that recurse in the ring buffer" depends on FTRACE_RECORD_RECURSION -- 2.43.0
