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 D90D24E5343; Fri, 9 Oct 2026 14:29:44 +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=1791556186; cv=none; b=pil4n7GTWCqPHAxSk5SznE94FkFHGLbj5qrobGKqQbrma9ODOPY77QZg0Ev0sobdCVLKj5L8xHwj9xyAn8VCVAfAIOm7TogsFhxBGrvKPAw/tJZ0q6ferrO30Y9dE9GCECwSkFqShlpg9fwX68KzUqBWgqHg0AF5r4GyS5A+JIs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791556186; c=relaxed/simple; bh=XjNzohxyIVrwD1sOZArSUHChdG7CZJC35mToRe9BluQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Bkxj0KL1qwhtTdY9MtVolREAQBo5nO57SSQ0LfTxuu2WU6mwzYlVtmoqpqVdEGyqle26fiYLs5OvBfBQATa1LidEW2JalOhx4/d3GlqsLy08T2n2ybb0FGxphEnrR7pfb+Gq98LpG7p7tidW0RMAwPaXcL8VCoVrsDlMJ2I/9mU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=F2BoNawv; 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="F2BoNawv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF9F41F000FF; Fri, 9 Oct 2026 14:29:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791556184; bh=naNw0hXzcBuVEJG7QiZZXw/bKvIND+lk/ncC8f8dlEE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=F2BoNawvTHF/wMa4KixV9Y7/F4s+dpk1CGZuge3ry7/6ll9sPTzCEy41lh6QVoI/d Cbt1UyJElHX1fn6JHsj+I4F3uBd4YXeBxBs0pTbyrfDfeBGAngaywDLLrEEibvD06c iTj2HmdAnrRtm1M7fx0OV+O5YMSG9A4BRj+nvc2E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Sashiko (nipa)" , Jamal Hadi Salim , Paolo Abeni , Sasha Levin Subject: [PATCH 7.2 134/428] net/sched: fq_codel: match the no-drop threshold to the packet size Date: Fri, 9 Oct 2026 16:07:51 +0200 Message-ID: <20261009140949.125409615@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261009140946.008206689@linuxfoundation.org> References: <20261009140946.008206689@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 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jamal Hadi Salim [ Upstream commit d031465acc362866f27e4f8f79cfecf1037fe2e5 ] commit d9ebd8f9aa8b ("net/sched: fq_codel: clamp default quantum and mtu") clamped both q->quantum and q->cparams.mtu to [256, FQ_CODEL_QUANTUM_MAX]. The two fields mean different things: quantum is a DRR credit that wants the 256 floor, but cparams.mtu is the CoDel no-drop threshold (codel_impl.h "*backlog <= params->mtu"). On a link whose maximum transmitted packet size is below 256, the floor extends CoDel's minimum-backlog exemption beyond one packet and delays drop or mark eligibility by several small packets. Split the clamp. quantum keeps [256, FQ_CODEL_QUANTUM_MAX]; cparams.mtu tracks psched_mtu() (the device MTU plus its hard-header length) with only the upper bound that guards the original overflow (psched_mtu() wrapping to ~2 GiB on a huge-MTU device). Conditions to recreate the bug: attach an fq_codel qdisc on a link whose MTU plus hard_header_len is below 256 (e.g. a CAN interface). At that MTU the no-drop threshold must equal the device MTU plus its hard-header length; before this patch it was forced to 256. Basic Testing done: with dev->mtu=100 and hard_header_len=14, a return probe on fq_codel_init() observed cparams.mtu change from 256 to 114 Fixes: d9ebd8f9aa8b ("net/sched: fq_codel: clamp default quantum and mtu") Reported-by: Sashiko (nipa) Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260819143136.57350-1-jhs@mojatatu.com Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/QDISC-34MS.v1.20260925165535@mojatatu.com Signed-off-by: Paolo Abeni Signed-off-by: Sasha Levin --- net/sched/sch_fq_codel.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/sched/sch_fq_codel.c b/net/sched/sch_fq_codel.c index 969b2510b0b86..e6c87a32950f9 100644 --- a/net/sched/sch_fq_codel.c +++ b/net/sched/sch_fq_codel.c @@ -517,8 +517,8 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt, q->flows_cnt = 1024; q->memory_limit = 32 << 20; /* 32 MBytes */ q->drop_batch_size = 64; - mtu = clamp_t(u32, psched_mtu(qdisc_dev(sch)), 256, FQ_CODEL_QUANTUM_MAX); - q->quantum = mtu; + mtu = min_t(u32, psched_mtu(qdisc_dev(sch)), FQ_CODEL_QUANTUM_MAX); + q->quantum = clamp_t(u32, mtu, 256, FQ_CODEL_QUANTUM_MAX); INIT_LIST_HEAD(&q->new_flows); INIT_LIST_HEAD(&q->old_flows); codel_params_init(&q->cparams); -- 2.53.0