From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C9645224D6; Sun, 7 Jun 2026 10:15:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780827304; cv=none; b=LL3a/kL2t7tqc3v6cdINQl+bDsWm3UMjyvhB36VcuIkLLMn7rG0wmooVXsTOS6roqjywNhJ52RuXspsjwayBL5O+fzIz7VarSUYqpJjfyTIeOaFNVwNQ00S5Y75B4sm+O86D4cC05Kllfser3NaeDviLzm5YyXQuk1HP2/Mb07Q= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780827304; c=relaxed/simple; bh=VNoHrLCtGV5bvX/6jaAQHDITF7Xkqji3X/Jd7QiBBZw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=obGk0+gG/xP+exlj4GPMW3/7hHShAgvvbbY7B8wsmNCuK2IDwPnfu2gCCRsf5zwVuymLNb/CVq80N38b5gJS0Ecm7YRycHppRYwgdPkJB7XbMjMbXPuX84sRRIOz6ztLHbxDH4L4ektMOZKiYSIkAlsIYBCXNoud8wwu6HSS0nQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=d49sloNL; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="d49sloNL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 049D41F00893; Sun, 7 Jun 2026 10:15:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780827303; bh=s3OPy2QVvKq1/cp9JAso6gio41IDkLV60eNcqYo8j80=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=d49sloNLyL2L8r3a+jdAZOuPikkfTm7SSx3r+HcBYf5gvky7p9xYYcmNAZYi7mOzT ahjjKIVbB9cNlGKdR9yEIqI7LPnsOKzPvWGWBBbJ8LtRRChcjwzWKW4rQ5Nd6LeSU5 lyPvEYahp0jyApC8/dCclkMIIgfm6qdX9J3++vGk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stephen Hemminger , Jamal Hadi Salim , Paolo Abeni , Sasha Levin Subject: [PATCH 7.0 081/332] net: Introduce skb tc depth field to track packet loops Date: Sun, 7 Jun 2026 11:57:30 +0200 Message-ID: <20260607095731.119198498@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260607095728.031258202@linuxfoundation.org> References: <20260607095728.031258202@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jamal Hadi Salim [ Upstream commit 98b34f3e8c3492cfc89ff943c9d92b4d52863d1d ] Add a 2-bit per-skb tc depth field to track packet loops across the stack. The previous per-CPU loop counters like MIRRED_NEST_LIMIT assume a single call stack and lose state in two cases: 1) When a packet is queued and reprocessed later (e.g., egress->ingress via backlog), the per-cpu state is gone by the time it is dequeued. 2) With XPS/RPS a packet may arrive on one CPU and be processed on another. A per-skb field solves both by travelling with the packet itself. The field fits in existing padding, using 2 bits that were previously a hole: pahole before(-) and after (+) diff looks like: __u8 slow_gro:1; /* 132: 3 1 */ __u8 csum_not_inet:1; /* 132: 4 1 */ __u8 unreadable:1; /* 132: 5 1 */ + __u8 tc_depth:2; /* 132: 6 1 */ - /* XXX 2 bits hole, try to pack */ /* XXX 1 byte hole, try to pack */ __u16 tc_index; /* 134 2 */ There used to be a ttl field which was removed as part of tc_verd in commit aec745e2c520 ("net-tc: remove unused tc_verd fields"). It was already unused by that time, due to remove earlier in commit c19ae86a510c ("tc: remove unused redirect ttl"). The first user of this field is netem, which increments tc_depth on duplicated packets before re-enqueueing them at the root qdisc. On re-entry, netem skips duplication for any skb with tc_depth already set, bounding recursion to a single level regardless of tree topology. The other user is mirred which increments it on each pass and limits to depth to MIRRED_DEFER_LIMIT (3). The new field was called ttl in earlier versions of this patch but renamed to tc_depth to avoid confusion with IP ttl. Note (looking at you Sashiko! Dont ignore me and continue bringing this up): 1. Since both mirred and netem utilize the same 2-bit tc_depth field it is possible when netem and mirred are used together that netem qdisc to skip the duplication step. This is a known trade-off, as a 2-bit field cannot independently track both features' recursion depths and it is not considered sane to have a setup that addresses both features on at the same time. 2. skb_scrub_packet does not clear tc_depth. This means a packet's loop history is preserved even across namespaces. While this might be restrictive for some topologies, it is also design intent to provide robustness against loops across namespaces. Reviewed-by: Stephen Hemminger Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260525122556.973584-2-jhs@mojatatu.com Signed-off-by: Paolo Abeni Stable-dep-of: db875221ab08 ("net/sched: Fix ethx:ingress -> ethy:egress -> ethx:ingress mirred loop") Signed-off-by: Sasha Levin --- include/linux/skbuff.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 2f278ce376b7ed..a58ff8903e536e 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -821,6 +821,7 @@ enum skb_tstamp_type { * @_sk_redir: socket redirection information for skmsg * @_nfct: Associated connection, if any (with nfctinfo bits) * @skb_iif: ifindex of device we arrived on + * @tc_depth: counter for packet duplication * @tc_index: Traffic control index * @hash: the packet hash * @queue_mapping: Queue mapping for multiqueue devices @@ -1030,6 +1031,7 @@ struct sk_buff { __u8 csum_not_inet:1; #endif __u8 unreadable:1; + __u8 tc_depth:2; #if defined(CONFIG_NET_SCHED) || defined(CONFIG_NET_XGRESS) __u16 tc_index; /* traffic control index */ #endif -- 2.53.0