From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8E4283ED13B for ; Thu, 17 Sep 2026 22:12:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789683126; cv=none; b=SPq9s2VrEH4xL1jgBUkNq6q9rW0b/y/y8bVhtb1U7uMBqYnex/Q//7/rva67ant8sva+v36BjV8Zf2fxNcX9T8AkhKafScoSkWY5oL4N7cPf+3vqTLp9VxtGeHj9o/6VuMch8wsdXLC0CAc9NRzY9IOgp4oKtjfD3Yk0lQXhcgA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789683126; c=relaxed/simple; bh=HIQv8brNzmzp6oSH9RiU8HsN+vHnBSGXSN47a34QNM0=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=UVUSSRtNwcN29zHrmDljg0a2vsuGNR8quik0t6TzCjlpnAqTAwcrFln03THJJyhePcgO3oHaGQaVCQYhfyKdV0aR5BkWTijyeQd7jBHmAG3Bizkct0J02BhxrSp9od2j5aR1n0UD4NRon7cwQkxdqhWyI44+DKopT9E5/dKKdIM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--kuniyu.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=ngs1+vCU; arc=none smtp.client-ip=209.85.215.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--kuniyu.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="ngs1+vCU" Received: by mail-pg1-f197.google.com with SMTP id 41be03b00d2f7-cbb92868263so24434a12.2 for ; Thu, 17 Sep 2026 15:12:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789683124; x=1790287924; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=2UYG2SrtB6EM+yhFk5h2ElEYvfaND8nBdx6rM334GIk=; b=ngs1+vCUWAaSiKuqwx09P1mHvPmabxs6PXwmUIfC41QNA234bkxVrswHB8SqQ7pR+C NNQXUEcKJrVPKwj/0pHTbO0HJ14RJFcx1+hsPzbpmzwEq6Dg+gQ29LNLamhdEMRScVD6 cmxO1TsEK7Gno9flHvUjy0yWhGAt+CPErwHB4wW19BYV3lRyS2G/vUSnnFl3lBn/Nb2q fp7/AJ3uvFWz5wTtnHWTORr/a9vXYn8VoX2DDi7hDCgDUxXYiP7v3tC5a9T2XTeD2phX 3ama0780iQY6ZpDdALFHFuLYsg+AtwUMKkR0/NjLr5fMzTnCptZRiw9NMsD1zcvJ1eFj XrRg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789683124; x=1790287924; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=2UYG2SrtB6EM+yhFk5h2ElEYvfaND8nBdx6rM334GIk=; b=s7btWj+Pc5zvP6J7uM584TX+qkoTOaJkegp64Y+B6eJiIAAOth2AruC+BXiWrEn75T q+bwAomNq0/AmAxm1gYopR0eWcqXtpsz3iAxwXwVq31LWbBgudYOalk34H9qbQ2uLjQg LzZZuQ3lHZkfnX/UDc5ntUdGqODpFPUPRh/1QXrmotarLwH8hVtMkAob/cqFElgSn00i hF7IeCsq+tjgiln0ZgJ7bpuYehRwcT74UgM1+M3z3dJAVGfT6wFmGHRwrJ3wSQ+cBuY6 iiZ93ruSUQXBC5fXmecDINohXp844Aa4/rOCP/XCWSz2qPC7elEvdNWldejFmKNZfSkE 5H6w== X-Forwarded-Encrypted: i=1; AKwUvBylQevUYSSVX6qJU7x8OlqBvDyJXsQXPRQrr76IwCyEV1qGr0Dy+fOz5iWScSY+/5sGe6E0FbAnX6Z4HmI=@vger.kernel.org X-Gm-Message-State: AFuF++lJgXvvMyYKskUCbUqhYGjNlpyuc5JyCIvck8cwgJlroB2iU+9J V2N2O1G69TEZQTmZGy44cmKoQOshkmrgdPX4r64AG6+4WPnVWzSaorRc4+CzhLYTq2HrzUZ9MCa G4xMBZQ== X-Received: from pgbj4-n1.prod.google.com ([2002:a05:6a02:61c4:10b0:cc4:c4f7:5c56]) (user=kuniyu job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:b8b:b0:3d3:adbf:7780 with SMTP id adf61e73a8af0-3dd8c41a009mr673980637.21.1789683123594; Thu, 17 Sep 2026 15:12:03 -0700 (PDT) Date: Thu, 17 Sep 2026 22:10:22 +0000 In-Reply-To: <20260917-hash-bucket-route-lists-v3-0-30493a37b6eb@cloudflare.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260917-hash-bucket-route-lists-v3-0-30493a37b6eb@cloudflare.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog Message-ID: <20260917221203.1811779-1-kuniyu@google.com> Subject: Re: [PATCH net-next v3 0/3] net: hash uncached route lists by device From: Kuniyuki Iwashima To: carges@cloudflare.com Cc: davem@davemloft.net, dsahern@kernel.org, edumazet@google.com, horms@kernel.org, idosch@nvidia.com, kernel-team@cloudflare.com, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org, pabeni@redhat.com, shuah@kernel.org Content-Type: text/plain; charset="UTF-8" From: Chris J Arges Date: Thu, 17 Sep 2026 14:38:21 -0500 > We have observed hung tasks blocked on rtnl_mutex while network namespaces > were being removed. The namespaces contained many network devices, and the > host had accumulated a large population of entries on the global per-CPU > uncached route lists. A perf profile collected during one incident > attributed most of the cleanup worker's samples to rt_flush_dev(): > > ``` > 99.92% kworker/u384:3- worker_thread > `-88.71% process_one_work > `-81.02% cleanup_net > `-81.00% unregister_netdevice_many_notify > `-79.42% notifier_call_chain > `-78.05% fib_netdev_event > `-77.92% rt_flush_dev > ``` > > For each device, rt_flush_dev() visits every possible CPU and scans the > global uncached route population while its caller holds rtnl_mutex. If N is > the number of devices, C the number of possible CPUs, and R the number of > uncached routes, the cost is O(N * (C + R)). > > During namespace cleanup, other processes that issue RTNETLINK operations > requiring the RTNL lock can stall until cleanup releases the lock. > > A minimal reproducer is available here: > https://github.com/arges/linux-reproducers/tree/main/rtnl-flush-storm > > This series replaces each per-CPU uncached route list with a hash table > using the network device as its key. Each table uses 64 buckets. This sounds a bit overkill. Also, this series still leaves O(N * C) loops. Given unregistering a single device is less common than destroying netns, I think the right approach should be to make the route flush once in cleanup_net() + outside RTNL. Could you try this change ? (only compile-tested) ---8<--- diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index 46b4c67e2966..d8ce7dc0fbdc 100644 --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -489,6 +489,7 @@ struct pernet_operations { */ int (*init)(struct net *net); void (*pre_exit)(struct net *net); + void (*pre_exit_batch)(struct list_head *net_exit_list); void (*exit)(struct net *net); void (*exit_batch)(struct list_head *net_exit_list); /* Following method is called with RTNL held. */ diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index da5f881fbd3b..7fc9bf45f3b6 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -160,6 +160,9 @@ static void ops_pre_exit_list(const struct pernet_operations *ops, list_for_each_entry(net, net_exit_list, exit_list) ops->pre_exit(net); } + + if (ops->pre_exit_batch) + ops->pre_exit_batch(net_exit_list); } static void ops_exit_rtnl_list(const struct list_head *ops_list, diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c index 8a3dc04e8cac..b8d76b6279e1 100644 --- a/net/ipv4/fib_frontend.c +++ b/net/ipv4/fib_frontend.c @@ -1685,6 +1685,11 @@ static void __net_exit fib_net_pre_exit(struct net *net) nl_fib_lookup_exit(net); } +static void __net_exit fib_net_pre_exit_batch(struct list_head *net_exit_list) +{ + rt_flush_dev(NULL); +} + static void __net_exit fib_net_exit_rtnl(struct net *net, struct list_head *dev_kill_list) { @@ -1704,6 +1709,7 @@ static void __net_exit fib_net_exit(struct net *net) static struct pernet_operations fib_net_ops = { .init = fib_net_init, .pre_exit = fib_net_pre_exit, + .pre_exit_batch = fib_net_pre_exit_batch, .exit_rtnl = fib_net_exit_rtnl, .exit = fib_net_exit, }; diff --git a/net/ipv4/route.c b/net/ipv4/route.c index d7da2f1acbb5..d35b66b33bbc 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1554,14 +1554,28 @@ struct uncached_list { static DEFINE_PER_CPU_ALIGNED(struct uncached_list, rt_uncached_list); +static void rt_replace_uncached_list(struct rtable *rt) +{ + struct net_device *dev = dst_dev(&rt->dst); + + rcu_assign_pointer(rt->dst.dev_rcu, blackhole_netdev); + netdev_ref_replace(dev, blackhole_netdev, + &rt->dst.dev_tracker, GFP_ATOMIC); +} + void rt_add_uncached_list(struct rtable *rt) { struct uncached_list *ul = raw_cpu_ptr(&rt_uncached_list); - rt->dst.rt_uncached_list = ul; - spin_lock_bh(&ul->lock); - list_add_tail(&rt->dst.rt_uncached, &ul->head); + + if (!check_net(dst_dev_net_rcu(&rt->dst))) { + rt_replace_uncached_list(rt); + } else { + rt->dst.rt_uncached_list = ul; + list_add_tail(&rt->dst.rt_uncached, &ul->head); + } + spin_unlock_bh(&ul->lock); } @@ -1587,6 +1601,9 @@ void rt_flush_dev(struct net_device *dev) struct rtable *rt, *safe; int cpu; + if (dev && !check_net(dev_net(dev))) + return; + for_each_possible_cpu(cpu) { struct uncached_list *ul = &per_cpu(rt_uncached_list, cpu); @@ -1595,11 +1612,11 @@ void rt_flush_dev(struct net_device *dev) spin_lock_bh(&ul->lock); list_for_each_entry_safe(rt, safe, &ul->head, dst.rt_uncached) { - if (rt->dst.dev != dev) + if (rt->dst.dev != dev && + (dev || check_net(dev_net(rt->dst.dev)))) continue; - rcu_assign_pointer(rt->dst.dev_rcu, blackhole_netdev); - netdev_ref_replace(dev, blackhole_netdev, - &rt->dst.dev_tracker, GFP_ATOMIC); + + rt_replace_uncached_list(rt); list_del_init(&rt->dst.rt_uncached); } spin_unlock_bh(&ul->lock); diff --git a/net/ipv6/route.c b/net/ipv6/route.c index 7535b09068a0..28233197e1e1 100644 --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -135,14 +135,35 @@ struct uncached_list { static DEFINE_PER_CPU_ALIGNED(struct uncached_list, rt6_uncached_list); +static void rt6_uncached_list_replace(struct rt6_info *rt) +{ + struct net_device *dev = dst_dev(&rt->dst); + struct inet6_dev *rt_idev = rt->rt6i_idev; + + if (rt_idev) { + rt->rt6i_idev = in6_dev_get(blackhole_netdev); + in6_dev_put(rt_idev); + } + + rcu_assign_pointer(rt->dst.dev_rcu, blackhole_netdev); + netdev_ref_replace(dev, blackhole_netdev, + &rt->dst.dev_tracker, + GFP_ATOMIC); +} + void rt6_uncached_list_add(struct rt6_info *rt) { struct uncached_list *ul = raw_cpu_ptr(&rt6_uncached_list); - rt->dst.rt_uncached_list = ul; - spin_lock_bh(&ul->lock); - list_add_tail(&rt->dst.rt_uncached, &ul->head); + + if (!check_net(dst_dev_net_rcu(&rt->dst))) { + rt6_uncached_list_replace(rt); + } else { + rt->dst.rt_uncached_list = ul; + list_add_tail(&rt->dst.rt_uncached, &ul->head); + } + spin_unlock_bh(&ul->lock); } @@ -161,6 +182,9 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev) { int cpu; + if (dev && !check_net(dev_net(dev))) + return; + for_each_possible_cpu(cpu) { struct uncached_list *ul = per_cpu_ptr(&rt6_uncached_list, cpu); struct rt6_info *rt, *safe; @@ -172,23 +196,17 @@ static void rt6_uncached_list_flush_dev(struct net_device *dev) list_for_each_entry_safe(rt, safe, &ul->head, dst.rt_uncached) { struct inet6_dev *rt_idev = rt->rt6i_idev; struct net_device *rt_dev = rt->dst.dev; - bool handled = false; - if (rt_idev && rt_idev->dev == dev) { - rt->rt6i_idev = in6_dev_get(blackhole_netdev); - in6_dev_put(rt_idev); - handled = true; + if (dev) { + if (rt_dev != dev && + (!rt_idev || rt_idev->dev != dev)) + continue; + } else if (check_net(dev_net(rt_dev))) { + continue; } - if (rt_dev == dev) { - rt->dst.dev = blackhole_netdev; - netdev_ref_replace(rt_dev, blackhole_netdev, - &rt->dst.dev_tracker, - GFP_ATOMIC); - handled = true; - } - if (handled) - list_del_init(&rt->dst.rt_uncached); + rt6_uncached_list_replace(rt); + list_del_init(&rt->dst.rt_uncached); } spin_unlock_bh(&ul->lock); } @@ -6795,6 +6813,11 @@ static int __net_init ip6_route_net_init(struct net *net) goto out; } +static void __net_exit ip6_route_net_pre_exit_batch(struct list_head *net_exit_list) +{ + rt6_uncached_list_flush_dev(NULL); +} + static void __net_exit ip6_route_net_exit(struct net *net) { kfree(net->ipv6.fib6_null_entry); @@ -6833,6 +6856,7 @@ static void __net_exit ip6_route_net_exit_late(struct net *net) static struct pernet_operations ip6_route_net_ops = { .init = ip6_route_net_init, + .pre_exit_batch = ip6_route_net_pre_exit_batch, .exit = ip6_route_net_exit, }; ---8<---