From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 2D31D35A2B8; Tue, 26 Aug 2025 14:44:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756219482; cv=none; b=gQIld7BGZJ+IF6Y7hw/4cUcQqS357zsNDvNyiismmQ5dkNlIpqbcLkF8EnTdQ1JnFmssQwsZJS0ApKs2SOP7Pu/IpHiigOL2Q59J9KGDfFdan8K8AGDfhgARB0/JCif+6wZ+3bxWSNajAU4vpJM+Xw4fmpsd3cNfFg591NC5IyA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756219482; c=relaxed/simple; bh=OJXu+y0TBNggLZEeCrDXR+1hOijy8rZfpklAur0PP98=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=G1glrjTeJ213bzd19oTWC2dVt7PmUKtKURELTbE59xJNNrjUoiQYMmWSzI4or0KbP3c8THXSZoEkLtHoZwSKEvxxy8fc3xRVZuAuvPj2UuELMXSb5dFvvSwhBmC6L1usw7L+LGmEV8S1rsUhTpAnA6UC/JS5EWQdonlri6asZdc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=TcYrGhxF; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="TcYrGhxF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6764FC4CEF1; Tue, 26 Aug 2025 14:44:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756219481; bh=OJXu+y0TBNggLZEeCrDXR+1hOijy8rZfpklAur0PP98=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TcYrGhxFCXPvS/u4hgDBJiAIRu3RLWBOEFkeit4eR9itM0tKKP1Sp7y1pKcARlfX0 aVph34xiWzt6lD/SpiSoisrUyF1dQjBXeU8m9ACSt0jkjh2ThZtooO3PtZQGPanFpX GRag0KQOBzr+URTkzE9hvWis4hrKiyTfKMa2Xy0Y= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, William Liu , Savino Dicanosa , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= , Jamal Hadi Salim , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.4 399/403] net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit Date: Tue, 26 Aug 2025 13:12:05 +0200 Message-ID: <20250826110918.057037683@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110905.607690791@linuxfoundation.org> References: <20250826110905.607690791@linuxfoundation.org> User-Agent: quilt/0.68 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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: William Liu [ Upstream commit 15de71d06a400f7fdc15bf377a2552b0ec437cf5 ] The following setup can trigger a WARNING in htb_activate due to the condition: !cl->leaf.q->q.qlen tc qdisc del dev lo root tc qdisc add dev lo root handle 1: htb default 1 tc class add dev lo parent 1: classid 1:1 \ htb rate 64bit tc qdisc add dev lo parent 1:1 handle f: \ cake memlimit 1b ping -I lo -f -c1 -s64 -W0.001 127.0.0.1 This is because the low memlimit leads to a low buffer_limit, which causes packet dropping. However, cake_enqueue still returns NET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an empty child qdisc. We should return NET_XMIT_CN when packets are dropped from the same tin and flow. I do not believe return value of NET_XMIT_CN is necessary for packet drops in the case of ack filtering, as that is meant to optimize performance, not to signal congestion. Fixes: 046f6fd5daef ("sched: Add Common Applications Kept Enhanced (cake) qdisc") Signed-off-by: William Liu Reviewed-by: Savino Dicanosa Acked-by: Toke Høiland-Jørgensen Reviewed-by: Jamal Hadi Salim Link: https://patch.msgid.link/20250819033601.579821-1-will@willsroot.io Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/sch_cake.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c index fc96ec46e6f6..738691b5697b 100644 --- a/net/sched/sch_cake.c +++ b/net/sched/sch_cake.c @@ -1725,7 +1725,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, ktime_t now = ktime_get(); struct cake_tin_data *b; struct cake_flow *flow; - u32 idx; + u32 idx, tin; /* choose flow to insert into */ idx = cake_classify(sch, &b, skb, q->flow_mode, &ret); @@ -1735,6 +1735,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, __qdisc_drop(skb, to_free); return ret; } + tin = (u32)(b - q->tins); idx--; flow = &b->flows[idx]; @@ -1904,13 +1905,22 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, q->buffer_max_used = q->buffer_used; if (q->buffer_used > q->buffer_limit) { + bool same_flow = false; u32 dropped = 0; + u32 drop_id; while (q->buffer_used > q->buffer_limit) { dropped++; - cake_drop(sch, to_free); + drop_id = cake_drop(sch, to_free); + + if ((drop_id >> 16) == tin && + (drop_id & 0xFFFF) == idx) + same_flow = true; } b->drop_overlimit += dropped; + + if (same_flow) + return NET_XMIT_CN; } return NET_XMIT_SUCCESS; } -- 2.50.1