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AJvYcCWoyZKO0L2iVZ3UWO24elNihlVKTuIXVHhiQ83Pb4RNstCDxXdduDqhX3GwBNePlWbLZu3ksjUd4p3qy7Jl2Xl/sI1FTeIc X-Gm-Message-State: AOJu0YxG99QmdYtM71a1Cv890ISBH8L02uW2pUmu84ykRaITisQGeQbA bZERP0xb6ZW7ycYwbS0JDcrkIRDDi6Rz1F1tk2uRLAh7xd8bR17QSowIqD9AS6smpyCUBBsb5Pj h4KeAgLS4mWfP73X+jDCXmuW6aGuf3ReC+JhQ X-Google-Smtp-Source: AGHT+IFEjiceN+yrYTYt1HpD4GLH2iz7RZ3fL9QB3wvfoxYiEhKMRXkCkHMrxMA/l4m98VU99iOPOBZLl5AlOnFkw7A= X-Received: by 2002:a81:ad24:0:b0:60c:c997:308e with SMTP id l36-20020a81ad24000000b0060cc997308emr12845667ywh.0.1710783409926; Mon, 18 Mar 2024 10:36:49 -0700 (PDT) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20240314111713.5979-1-renmingshuai@huawei.com> In-Reply-To: From: Jamal Hadi Salim Date: Mon, 18 Mar 2024 13:36:38 -0400 Message-ID: Subject: Re: [PATCH] net/sched: Forbid assigning mirred action to a filter attached to the egress To: Eric Dumazet Cc: renmingshuai , xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net, vladbu@nvidia.com, netdev@vger.kernel.org, yanan@huawei.com, liaichun@huawei.com, caowangbao@huawei.com, Eric Dumazet , Jakub Kicinski , Paolo Abeni , Victor Nogueira , Pedro Tammela Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Mar 18, 2024 at 11:46=E2=80=AFAM Eric Dumazet = wrote: > > On Mon, Mar 18, 2024 at 3:27=E2=80=AFPM Jamal Hadi Salim wrote: > > > > On Sun, Mar 17, 2024 at 12:10=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > On Thu, Mar 14, 2024 at 1:14=E2=80=AFPM Jamal Hadi Salim wrote: > > > > > > > > On Thu, Mar 14, 2024 at 7:18=E2=80=AFAM renmingshuai wrote: > > > > > > > > > > As we all know the mirred action is used to mirroring or redirect= ing the > > > > > packet it receives. Howerver, add mirred action to a filter attac= hed to > > > > > a egress qdisc might cause a deadlock. To reproduce the problem, = perform > > > > > the following steps: > > > > > (1)tc qdisc add dev eth0 root handle 1: htb default 30 \n > > > > > (2)tc filter add dev eth2 protocol ip prio 2 flower verbose \ > > > > > action police rate 100mbit burst 12m conform-exceed jump 1 \ > > > > > / pipe mirred egress redirect dev eth2 action drop > > > > > > > > > > > > > I think you meant both to be the same device eth0 or eth2? > > > > > > > > > The stack is show as below: > > > > > [28848.883915] _raw_spin_lock+0x1e/0x30 > > > > > [28848.884367] __dev_queue_xmit+0x160/0x850 > > > > > [28848.884851] ? 0xffffffffc031906a > > > > > [28848.885279] tcf_mirred_act+0x3ab/0x596 [act_mirred] > > > > > [28848.885863] tcf_action_exec.part.0+0x88/0x130 > > > > > [28848.886401] fl_classify+0x1ca/0x1e0 [cls_flower] > > > > > [28848.886970] ? dequeue_entity+0x145/0x9e0 > > > > > [28848.887464] ? newidle_balance+0x23f/0x2f0 > > > > > [28848.887973] ? nft_lookup_eval+0x57/0x170 [nf_tables] > > > > > [28848.888566] ? nft_do_chain+0xef/0x430 [nf_tables] > > > > > [28848.889137] ? __flush_work.isra.0+0x35/0x80 > > > > > [28848.889657] ? nf_ct_get_tuple+0x1cf/0x210 [nf_conntrack] > > > > > [28848.890293] ? do_select+0x637/0x870 > > > > > [28848.890735] tcf_classify+0x52/0xf0 > > > > > [28848.891177] htb_classify+0x9d/0x1c0 [sch_htb] > > > > > [28848.891722] htb_enqueue+0x3a/0x1c0 [sch_htb] > > > > > [28848.892251] __dev_queue_xmit+0x2d8/0x850 > > > > > [28848.892738] ? nf_hook_slow+0x3c/0xb0 > > > > > [28848.893198] ip_finish_output2+0x272/0x580 > > > > > [28848.893692] __ip_queue_xmit+0x193/0x420 > > > > > [28848.894179] __tcp_transmit_skb+0x8cc/0x970 > > > > > > > > > > In this case, the process has hold the qdisc spin lock in __dev_q= ueue_xmit > > > > > before the egress packets are mirred, and it will attempt to obta= in the > > > > > spin lock again after packets are mirred, which cause a deadlock. > > > > > > > > > > Fix the issue by forbidding assigning mirred action to a filter a= ttached > > > > > to the egress. > > > > > > > > > > Signed-off-by: Mingshuai Ren > > > > > --- > > > > > net/sched/act_mirred.c | 4 +++ > > > > > .../tc-testing/tc-tests/actions/mirred.json | 32 +++++++++++++= ++++++ > > > > > 2 files changed, 36 insertions(+) > > > > > > > > > > diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c > > > > > index 5b3814365924..fc96705285fb 100644 > > > > > --- a/net/sched/act_mirred.c > > > > > +++ b/net/sched/act_mirred.c > > > > > @@ -120,6 +120,10 @@ static int tcf_mirred_init(struct net *net, = struct nlattr *nla, > > > > > NL_SET_ERR_MSG_MOD(extack, "Mirred requires attri= butes to be passed"); > > > > > return -EINVAL; > > > > > } > > > > > + if (tp->chain->block->q->parent !=3D TC_H_INGRESS) { > > > > > + NL_SET_ERR_MSG_MOD(extack, "Mirred can only be as= signed to the filter attached to ingress"); > > > > > + return -EINVAL; > > > > > + } > > > > > > > > Sorry, this is too restrictive as Jiri said. We'll try to reproduce= . I > > > > am almost certain this used to work in the old days. > > > > > > Ok, i looked at old notes - it did work at "some point" pre-tdc. > > > Conclusion is things broke around this time frame: > > > https://lore.kernel.org/netdev/1431679850-31896-1-git-send-email-fw@s= trlen.de/ > > > https://lore.kernel.org/netdev/1465095748.2968.45.camel@edumazet-glap= top3.roam.corp.google.com/ > > > > > > Looking further into it. > > > > This is what we came up with. Eric, please take a look... > > > > cheers, > > jamal > > > > > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -3789,7 +3789,14 @@ static inline int __dev_xmit_skb(struct sk_buff > > *skb, struct Qdisc *q, > > if (unlikely(contended)) > > spin_lock(&q->busylock); > > > > + if (dev_recursion_level()) { > > I am not sure what your intent is, but this seems wrong to me. > There is a deadlock if you reenter the same device which has a qdisc attached to it more than once. Essentially entering __dev_xmit_skb() we grab the root qdisc lock then run some action which requires it to grab the root qdisc lock (again). This is easy to show with mirred (although i am wondering if syzkaller may have produced this at some point).. $TC qdisc add dev $DEV root handle 1: htb default 1 $TC filter add dev $DEV protocol ip u32 match ip protocol 1 0xff action mirred egress mirror dev $DEV Above example is essentially egress $DEV-> egress $DEV in both cases "egress $DEV" grabs the root qdisc lock. You could also create another example with egress($DEV1->$DEV2->back to $DEV1). > Some valid setup use : > > A bonding device, with HTB qdisc (or other qdisc) > (This also could be a tunnel device with a qdisc) > > -> one or multiple physical NIC, wth FQ or other qdisc. > > Packets would be dropped here when we try to reach the physical device. > If you have an example handy please send it. I am trying to imagine how those would have worked if they have to reenter the root qdisc of the same dev multiple times.. cheers, jamal > > + rc =3D NET_XMIT_DROP; > > + __qdisc_drop(skb, &to_free); > > + goto free; > > + } > > + > > spin_lock(root_lock); > > + dev_xmit_recursion_inc(); > > if (unlikely(test_bit(__QDISC_STATE_DEACTIVATED, &q->state))) { > > __qdisc_drop(skb, &to_free); > > rc =3D NET_XMIT_DROP; > > @@ -3824,8 +3831,10 @@ static inline int __dev_xmit_skb(struct sk_buff > > *skb, struct Qdisc *q, > > qdisc_run_end(q); > > } > > } > > + dev_xmit_recursion_dec(); > > spin_unlock(root_lock); > > if (unlikely(to_free)) > > +free: > > kfree_skb_list_reason(to_free, > > tcf_get_drop_reason(to_free)); > > if (unlikely(contended))