netdev - [PATCH v1] net/sched: sch_qfq: Avoid triggering might_sleep in atomic context in qfq_delete

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Message-ID: <20250717230128.159766-1-xmei5@asu.edu>
Date: Thu, 17 Jul 2025 16:01:28 -0700
From: Xiang Mei <xmei5@....edu>
To: dan.carpenter@...aro.org
Cc: xiyou.wangcong@...il.com,
	netdev@...r.kernel.org,
	Xiang Mei <xmei5@....edu>
Subject: [PATCH v1] net/sched: sch_qfq: Avoid triggering might_sleep in atomic context in qfq_delete_class

might_sleep could be trigger in the atomic context in qfq_delete_class.

qfq_destroy_class was moved into atomic context locked
by sch_tree_lock to avoid a race condition bug on
qfq_aggregate. However, might_sleep could be triggered by
qfq_destroy_class, which introduced sleeping in atomic context (path:
qfq_destroy_class->qdisc_put->__qdisc_destroy->lockdep_unregister_key
->might_sleep).

Considering the race is on the qfq_aggregate objects, keeping
qfq_rm_from_agg in the lock but moving the left part out can solve
this issue.

Fixes: 5e28d5a3f774 ("net/sched: sch_qfq: Fix race condition on qfq_aggregate")
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Signed-off-by: Xiang Mei <xmei5@....edu>
Link: https://patch.msgid.link/4a04e0cc-a64b-44e7-9213-2880ed641d77@sabinyo.mountain
---
v1: Avoid might_sleep in atomic context

 net/sched/sch_qfq.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/sched/sch_qfq.c b/net/sched/sch_qfq.c
index f0eb70353744..2255355e51d3 100644
--- a/net/sched/sch_qfq.c
+++ b/net/sched/sch_qfq.c
@@ -536,9 +536,6 @@ static int qfq_change_class(struct Qdisc *sch, u32 classid, u32 parentid,
 
 static void qfq_destroy_class(struct Qdisc *sch, struct qfq_class *cl)
 {
-	struct qfq_sched *q = qdisc_priv(sch);
-
-	qfq_rm_from_agg(q, cl);
 	gen_kill_estimator(&cl->rate_est);
 	qdisc_put(cl->qdisc);
 	kfree(cl);
@@ -559,10 +556,11 @@ static int qfq_delete_class(struct Qdisc *sch, unsigned long arg,
 
 	qdisc_purge_queue(cl->qdisc);
 	qdisc_class_hash_remove(&q->clhash, &cl->common);
-	qfq_destroy_class(sch, cl);
+	qfq_rm_from_agg(q, cl);
 
 	sch_tree_unlock(sch);
 
+	qfq_destroy_class(sch, cl);
 	return 0;
 }
 
@@ -1503,6 +1501,7 @@ static void qfq_destroy_qdisc(struct Qdisc *sch)
 	for (i = 0; i < q->clhash.hashsize; i++) {
 		hlist_for_each_entry_safe(cl, next, &q->clhash.hash[i],
 					  common.hnode) {
+			qfq_rm_from_agg(q, cl);
 			qfq_destroy_class(sch, cl);
 		}
 	}
-- 
2.43.0