From 8e014b654d9e51abed132155237d855b25da06a0 Mon Sep 17 00:00:00 2001 From: Menglong Dong Date: Thu, 11 Aug 2022 20:07:08 +0800 Subject: [PATCH] net: skb: prevent the split of kfree_skb_reason() by gcc Sometimes, gcc will optimize the function by spliting it to two or more functions. In this case, kfree_skb_reason() is splited to kfree_skb_reason and kfree_skb_reason.part.0. However, the function/tracepoint trace_kfree_skb() in it needs the return address of kfree_skb_reason(). This split makes the call chains becomes: kfree_skb_reason() -> kfree_skb_reason.part.0 -> trace_kfree_skb() which makes the return address that passed to trace_kfree_skb() be kfree_skb(). Therefore, prevent this kind of optimization to kfree_skb_reason() by making the optimize level to "O1". I think these should be better method instead of this "O1", but I can't figure it out...... This optimization CAN happen, which depend on the behavior of gcc. I'm not able to reproduce it in the latest kernel code, but it happens in my kernel of version 5.4.119. Maybe the latest code already do someting that prevent this happen? Signed-off-by: Menglong Dong --- include/linux/compiler_attributes.h | 2 ++ net/core/skbuff.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index 445e80517cab68..51f7c13bca98cb 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -371,4 +371,6 @@ */ #define __weak __attribute__((__weak__)) +#define __nofnsplit __attribute__((optimize("O1"))) + #endif /* __LINUX_COMPILER_ATTRIBUTES_H */ diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 974bbbbe7138a4..ff9ccbc032b924 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -777,7 +777,8 @@ EXPORT_SYMBOL(__kfree_skb); * hit zero. Meanwhile, pass the drop reason to 'kfree_skb' * tracepoint. */ -void kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason) +void __nofnsplit +kfree_skb_reason(struct sk_buff *skb, enum skb_drop_reason reason) { if (!skb_unref(skb)) return;