On Wed, 3 Apr 2024 15:03:27 -0700 Andrii Nakryiko <andrii@xxxxxxxxxx> wrote: > 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/ > This looks good to me :) Acked-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> Thank you, > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> > Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> > Cc: Paul E. McKenney <paulmck@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 > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
