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Message-ID: <73065927a49619fcd60e5b765c929f899a66cd1a.1701853200.git.dcaratti@redhat.com>
Date: Wed, 6 Dec 2023 10:03:12 +0100
From: Davide Caratti <dcaratti@...hat.com>
To: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Jamal Hadi Salim <jhs@...atatu.com>,
Cong Wang <xiyou.wangcong@...il.com>,
Jiri Pirko <jiri@...nulli.us>
Cc: netdev@...r.kernel.org,
xmu@...hat.com,
cpaasch@...le.com
Subject: [PATCH net-next] net/sched: fix false lockdep warning on qdisc root lock
Xiumei and Cristoph reported the following lockdep splat, it complains of
the qdisc root being taken twice:
============================================
WARNING: possible recursive locking detected
6.7.0-rc3+ #598 Not tainted
--------------------------------------------
swapper/2/0 is trying to acquire lock:
ffff888177190110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70
but task is already holding lock:
ffff88811995a110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&sch->q.lock);
lock(&sch->q.lock);
*** DEADLOCK ***
May be due to missing lock nesting notation
5 locks held by swapper/2/0:
#0: ffff888135a09d98 ((&in_dev->mr_ifc_timer)){+.-.}-{0:0}, at: call_timer_fn+0x11a/0x510
#1: ffffffffaaee5260 (rcu_read_lock){....}-{1:2}, at: ip_finish_output2+0x2c0/0x1ed0
#2: ffffffffaaee5200 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x209/0x2e70
#3: ffff88811995a110 (&sch->q.lock){+.-.}-{2:2}, at: __dev_queue_xmit+0x1560/0x2e70
#4: ffffffffaaee5200 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x209/0x2e70
stack backtrace:
CPU: 2 PID: 0 Comm: swapper/2 Not tainted 6.7.0-rc3+ #598
Hardware name: Red Hat KVM, BIOS 1.13.0-2.module+el8.3.0+7353+9de0a3cc 04/01/2014
Call Trace:
<IRQ>
dump_stack_lvl+0x4a/0x80
__lock_acquire+0xfdd/0x3150
lock_acquire+0x1ca/0x540
_raw_spin_lock+0x34/0x80
__dev_queue_xmit+0x1560/0x2e70
tcf_mirred_act+0x82e/0x1260 [act_mirred]
tcf_action_exec+0x161/0x480
tcf_classify+0x689/0x1170
prio_enqueue+0x316/0x660 [sch_prio]
dev_qdisc_enqueue+0x46/0x220
__dev_queue_xmit+0x1615/0x2e70
ip_finish_output2+0x1218/0x1ed0
__ip_finish_output+0x8b3/0x1350
ip_output+0x163/0x4e0
igmp_ifc_timer_expire+0x44b/0x930
call_timer_fn+0x1a2/0x510
run_timer_softirq+0x54d/0x11a0
__do_softirq+0x1b3/0x88f
irq_exit_rcu+0x18f/0x1e0
sysvec_apic_timer_interrupt+0x6f/0x90
</IRQ>
This happens when TC does a mirred egress redirect from the root qdisc of
device A to the root qdisc of device B. As long as these two locks aren't
protecting the same qdisc, they can be acquired in chain: add a per-qdisc
lockdep class to silence false warnings.
CC: Xiumei Mu <xmu@...hat.com>
Reported-by: Cristoph Paasch <cpaasch@...le.com>
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/451
Signed-off-by: Davide Caratti <dcaratti@...hat.com>
---
include/net/sch_generic.h | 1 +
net/sched/sch_generic.c | 3 +++
2 files changed, 4 insertions(+)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index dcb9160e6467..a395ca76066c 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -126,6 +126,7 @@ struct Qdisc {
struct rcu_head rcu;
netdevice_tracker dev_tracker;
+ struct lock_class_key root_lock_key;
/* private data */
long privdata[] ____cacheline_aligned;
};
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 8dd0e5925342..da3e1ea42852 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -944,7 +944,9 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
__skb_queue_head_init(&sch->gso_skb);
__skb_queue_head_init(&sch->skb_bad_txq);
gnet_stats_basic_sync_init(&sch->bstats);
+ lockdep_register_key(&sch->root_lock_key);
spin_lock_init(&sch->q.lock);
+ lockdep_set_class(&sch->q.lock, &sch->root_lock_key);
if (ops->static_flags & TCQ_F_CPUSTATS) {
sch->cpu_bstats =
@@ -1064,6 +1066,7 @@ static void __qdisc_destroy(struct Qdisc *qdisc)
if (ops->destroy)
ops->destroy(qdisc);
+ lockdep_unregister_key(&qdisc->root_lock_key);
module_put(ops->owner);
netdev_put(qdisc_dev(qdisc), &qdisc->dev_tracker);
--
2.41.0
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