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: 5e28d5a ("net/sched: sch_qfq: Fix race condition on qfq_aggregate")
Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Xiang Mei <[email protected]>
Link: https://patch.msgid.link/[email protected]
Reviewed-by: Cong Wang <[email protected]>
Reviewed-by: Dan Carpenter <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Author: n132

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);
 		}
 	}