From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 57C5EC25B06 for ; Fri, 12 Aug 2022 02:50:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236876AbiHLCu0 (ORCPT ); Thu, 11 Aug 2022 22:50:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54054 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234955AbiHLCuZ (ORCPT ); Thu, 11 Aug 2022 22:50:25 -0400 Received: from mail-pj1-x1041.google.com (mail-pj1-x1041.google.com [IPv6:2607:f8b0:4864:20::1041]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6AE161900C; Thu, 11 Aug 2022 19:50:24 -0700 (PDT) Received: by mail-pj1-x1041.google.com with SMTP id c19-20020a17090ae11300b001f2f94ed5c6so6423938pjz.1; Thu, 11 Aug 2022 19:50:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc; bh=AIZvVMlGU+8xrlIg+scbeMLPAQHdI3AkHz0T/txqtNA=; b=DGf6fG+qqPqdY+ER0VAY7JrdJJRDfmzwHKOLYJoRKubxbKQ6HNu13Q0qgR2hGZYsNV bmhnQ7yZzJHH3t0O0s2JXrlqrepr3ipj3b98IIj4z6ANN9LWm8ST7qfaKqNT4zEpOLrU TP63WqhM2NYGAW4vYPktRa60REziaI1tAYGierATVok4Cd3HWgvPucknxuWi5EA7Pba+ RYGBWwXWjZO5EC3lu2pBdfFFQtusYvUTaAtpgqtyTvOmVrDmOkY3g6PCNLwu1jMJ+Dk7 g1sUyQpuTqkRMdjVMWCw/orRqdQ4zkyjULeoEIjVoiyHfsXBTEicWn33lUtX/1dEBX5H 0IXA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc; bh=AIZvVMlGU+8xrlIg+scbeMLPAQHdI3AkHz0T/txqtNA=; b=nA7i5NF9sL2rLqPqcRlHYV4XEj3QZ0e+vqHqdPkav5EFHcX4e5FKAe7tHaf5id7bgJ uhRXMQbPJtKpb6WVCCu2i8n/jOBFtB88aELz5/YFzBlTEBM3KqXPD1yriKjm+bFpxUjH 7RCALBnulMYZ1CAbueMM995NQ/j3ka+X0uqvf8r61NWtSpMpRXULPi728x4EFk856O8I PAZBtlhaRm+NgAuX5flw19XIBQiCM/bF79LiXWO/4srYdG432OF632mcapJ9gSDD7ydc GPrhwXzc95fCfwUHaKGyGX72NaxKxQYuqVrucgmDyKTJpsRJSlicBYV6NjoZUq6NixVX G+MQ== X-Gm-Message-State: ACgBeo0YKOBvBHOGxKOedmLEzCk3NboIS85BTfro1j13m6fZPp/q0hJO mOgp2zlJjV/1YTlFzb6qSRA= X-Google-Smtp-Source: AA6agR51hCmeIyVEXVanfRYhNzx8TGQC5AudmRgTc4ZXlTynvqd8tV4xXPuaRPTDW+m1wi0zVQaLvw== X-Received: by 2002:a17:902:d502:b0:171:47c7:a62b with SMTP id b2-20020a170902d50200b0017147c7a62bmr2070614plg.117.1660272623878; Thu, 11 Aug 2022 19:50:23 -0700 (PDT) Received: from localhost.localdomain ([203.205.141.25]) by smtp.gmail.com with ESMTPSA id u186-20020a6260c3000000b0052ab42ea0c5sm422460pfb.147.2022.08.11.19.50.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Aug 2022 19:50:23 -0700 (PDT) From: menglong8.dong@gmail.com X-Google-Original-From: imagedong@tencent.com To: kuba@kernel.org, miguel.ojeda.sandonis@gmail.com Cc: ojeda@kernel.org, ndesaulniers@google.com, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, asml.silence@gmail.com, imagedong@tencent.com, luiz.von.dentz@intel.com, vasily.averin@linux.dev, jk@codeconstruct.com.au, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: [PATCH net-next v2] net: skb: prevent the split of kfree_skb_reason() by gcc Date: Fri, 12 Aug 2022 10:50:15 +0800 Message-Id: <20220812025015.316609-1-imagedong@tencent.com> X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Menglong Dong 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 --- v2: - replace 'optimize' with '__optimize__' in __nofnsplit, as Miguel Ojeda advised. --- 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 445e80517cab..b910b5775fc7 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -270,6 +270,8 @@ */ #define __noreturn __attribute__((__noreturn__)) +#define __nofnsplit __attribute__((__optimize__("O1"))) + /* * Optional: not supported by gcc. * Optional: not supported by icc. diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 974bbbbe7138..ff9ccbc032b9 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; -- 2.36.1