[PATCH 6.8 048/158] net/sched: Fix mirred deadlock on device recursion

Greg Kroah-Hartman
2024-04-23T21:41:19Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 0f022d32c3eca477fbf79a205243a6123ed0fe11 ]

When the mirred action is used on a classful egress qdisc and a packet is
mirrored or redirected to self we hit a qdisc lock deadlock.
See trace below.

[..... other info removed for brevity....]
[ 82.890906]
[ 82.890906] ============================================
[ 82.890906] WARNING: possible recursive locking detected
[ 82.890906] 6.8.0-05205-g77fadd89fe2d-dirty #213 Tainted: G W
[ 82.890906] --------------------------------------------
[ 82.890906] ping/418 is trying to acquire lock:
[ 82.890906] ffff888006994110 (&sch->q.lock){+.-.}-{3:3}, at:
__dev_queue_xmit+0x1778/0x3550
[ 82.890906]
[ 82.890906] but task is already holding lock:
[ 82.890906] ffff888006994110 (&sch->q.lock){+.-.}-{3:3}, at:
__dev_queue_xmit+0x1778/0x3550
[ 82.890906]
[ 82.890906] other info that might help us debug this:
[ 82.890906] Possible unsafe locking scenario:
[ 82.890906]
[ 82.890906] CPU0
[ 82.890906] ----
[ 82.890906] lock(&sch->q.lock);
[ 82.890906] lock(&sch->q.lock);
[ 82.890906]
[ 82.890906] *** DEADLOCK ***
[ 82.890906]
[..... other info removed for brevity....]

Example setup (eth0->eth0) to recreate
tc qdisc add dev eth0 root handle 1: htb default 30
tc filter add dev eth0 handle 1: protocol ip prio 2 matchall \
action mirred egress redirect dev eth0

Another example(eth0->eth1->eth0) to recreate
tc qdisc add dev eth0 root handle 1: htb default 30
tc filter add dev eth0 handle 1: protocol ip prio 2 matchall \
action mirred egress redirect dev eth1

tc qdisc add dev eth1 root handle 1: htb default 30
tc filter add dev eth1 handle 1: protocol ip prio 2 matchall \
action mirred egress redirect dev eth0

We fix this by adding an owner field (CPU id) to struct Qdisc set after
root qdisc is entered. When the softirq enters it a second time, if the
qdisc owner is the same CPU, the packet is dropped to break the loop.

Reported-by: Mingshuai Ren <renmingshuai@huawei.com>
Closes: https://lore.kernel.org/netdev/20240314111713.5979-1-renmingshuai@huawei.com/
Fixes: 3bcb846ca4cf ("net: get rid of spin_trylock() in net_tx_action()")
Fixes: e578d9c02587 ("net: sched: use counter to break reclassify loops")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Victor Nogueira <victor@mojatatu.com>
Reviewed-by: Pedro Tammela <pctammela@mojatatu.com>
Tested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20240415210728.36949-1-victor@mojatatu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/net/sch_generic.h | 1 +
net/core/dev.c | 6 ++++++
net/sched/sch_generic.c | 1 +
3 files changed, 8 insertions(+)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index cefe0c4bdae34..41ca14e81d55f 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -117,6 +117,7 @@ struct Qdisc {
struct qdisc_skb_head q;
struct gnet_stats_basic_sync bstats;
struct gnet_stats_queue qstats;
+ int owner;
unsigned long state;
unsigned long state2; /* must be written under qdisc spinlock */
struct Qdisc *next_sched;
diff --git a/net/core/dev.c b/net/core/dev.c
index c9b8412f1c9d3..c365aa06f886f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3791,6 +3791,10 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
return rc;
}

+ if (unlikely(READ_ONCE(q->owner) == smp_processor_id())) {
+ kfree_skb_reason(skb, SKB_DROP_REASON_TC_RECLASSIFY_LOOP);
+ return NET_XMIT_DROP;
+ }
/*
* Heuristic to force contended enqueues to serialize on a
* separate lock before trying to get qdisc main lock.
@@ -3830,7 +3834,9 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
qdisc_run_end(q);
rc = NET_XMIT_SUCCESS;
} else {
+ WRITE_ONCE(q->owner, smp_processor_id());
rc = dev_qdisc_enqueue(skb, q, &to_free, txq);
+ WRITE_ONCE(q->owner, -1);
if (qdisc_run_begin(q)) {
if (unlikely(contended)) {
spin_unlock(&q->busylock);
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 9b3e9262040b6..a498b5d7c5d60 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -973,6 +973,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
sch->enqueue = ops->enqueue;
sch->dequeue = ops->dequeue;
sch->dev_queue = dev_queue;
+ sch->owner = -1;
netdev_hold(dev, &sch->dev_tracker, GFP_KERNEL);
refcount_set(&sch->refcnt, 1);

--
2.43.0