From: Andrii Nakryiko <andrii@kernel.org>
To: linux-trace-kernel@vger.kernel.org, rostedt@goodmis.org,
mhiramat@kernel.org
Cc: bpf@vger.kernel.org, jolsa@kernel.org,
Andrii Nakryiko <andrii@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH v3 1/2] ftrace: make extra rcu_is_watching() validation check optional
Date: Wed, 3 Apr 2024 15:03:27 -0700 [thread overview]
Message-ID: <20240403220328.455786-1-andrii@kernel.org> (raw)
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@mail.gmail.com/
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
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
next reply other threads:[~2024-04-03 22:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-03 22:03 Andrii Nakryiko [this message]
2024-04-03 22:03 ` [PATCH v3 2/2] rethook: honor CONFIG_FTRACE_VALIDATE_RCU_IS_WATCHING in rethook_try_get() Andrii Nakryiko
2024-04-09 22:48 ` Masami Hiramatsu
2024-04-18 18:41 ` Andrii Nakryiko
2024-04-09 22:49 ` [PATCH v3 1/2] ftrace: make extra rcu_is_watching() validation check optional Masami Hiramatsu
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