netdev - [PATCH 1/2] compiler_types: Add noinline_for

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Message-Id: <20241024093742.87681-2-laoar.shao@gmail.com>
Date: Thu, 24 Oct 2024 17:37:41 +0800
From: Yafang Shao <laoar.shao@...il.com>
To: edumazet@...gle.com,
	davem@...emloft.net,
	dsahern@...nel.org,
	kuba@...nel.org,
	pabeni@...hat.com
Cc: netdev@...r.kernel.org,
	Yafang Shao <laoar.shao@...il.com>
Subject: [PATCH 1/2] compiler_types: Add noinline_for_tracing annotation

Kernel functions that are not inlined can be easily hooked with BPF for
tracing. However, functions intended for tracing may still be inlined
unexpectedly. For example, in our case, after upgrading the compiler from
GCC 9 to GCC 11, the tcp_drop_reason() function was inlined, which broke
our monitoring tools. To prevent this, we need to ensure that the function
remains non-inlined.

The noinline_for_tracing annotation is introduced as a general solution for
preventing inlining of kernel functions that need to be traced. This
approach avoids the need for adding individual noinline comments to each
function and provides a more consistent way to maintain traceability.

Link: https://lore.kernel.org/netdev/CANn89iKvr44ipuRYFaPTpzwz=B_+pgA94jsggQ946mjwreV6Aw@mail.gmail.com/
Suggested-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Yafang Shao <laoar.shao@...il.com>
---
 include/linux/compiler_types.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 1a957ea2f4fe..0c8b9601e603 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -265,6 +265,12 @@ struct ftrace_likely_data {
  */
 #define noinline_for_stack noinline

+/*
+ * Use noinline_for_tracing for functions that should not be inlined.
+ * For tracing reasons.
+ */
+#define noinline_for_tracing noinline
+
 /*
  * Sanitizer helper attributes: Because using __always_inline and
  * __no_sanitize_* conflict, provide helper attributes that will either expand
-- 
2.43.5