Revert "net: sched: fq_codel: remove redundant resource cleanup in fq_codel_init()"

This reverts commit 494f5063.

When the default qdisc is fq_codel, if the qdisc of dev_queue fails to be
inited during mqprio_init(), fq_codel_reset() is invoked to clear
resources. In this case, the flow is NULL, and it will cause gpf issue.

The process is as follows:
qdisc_create_dflt()
	fq_codel_init()
		...
		q->flows_cnt = 1024;
		...
		q->flows = kvcalloc(...)      --->failed, q->flows is NULL
	...
	qdisc_put()
		...
		fq_codel_reset()
			...
			flow = q->flows + i   --->q->flows is NULL

The following is the Call Trace information:
general protection fault, probably for non-canonical address
0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
RIP: 0010:fq_codel_reset+0x14d/0x350
Call Trace:
<TASK>
qdisc_reset+0xed/0x6f0
qdisc_destroy+0x82/0x4c0
qdisc_put+0x9e/0xb0
qdisc_create_dflt+0x2c3/0x4a0
mqprio_init+0xa71/0x1760
qdisc_create+0x3eb/0x1000
tc_modify_qdisc+0x408/0x1720
rtnetlink_rcv_msg+0x38e/0xac0
netlink_rcv_skb+0x12d/0x3a0
netlink_unicast+0x4a2/0x740
netlink_sendmsg+0x826/0xcc0
sock_sendmsg+0xc5/0x100
____sys_sendmsg+0x583/0x690
___sys_sendmsg+0xe8/0x160
__sys_sendmsg+0xbf/0x160
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7fd272b22d04
</TASK>
Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/sch_fq_codel.c

@@ -478,24 +478,26 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt,
 	if (opt) {
 		err = fq_codel_change(sch, opt, extack);
 		if (err)
-			return err;
+			goto init_failure;
 	}
 
 	err = tcf_block_get(&q->block, &q->filter_list, sch, extack);
 	if (err)
-		return err;
+		goto init_failure;
 
 	if (!q->flows) {
 		q->flows = kvcalloc(q->flows_cnt,
 				    sizeof(struct fq_codel_flow),
 				    GFP_KERNEL);
-		if (!q->flows)
-			return -ENOMEM;
-
+		if (!q->flows) {
+			err = -ENOMEM;
+			goto init_failure;
+		}
 		q->backlogs = kvcalloc(q->flows_cnt, sizeof(u32), GFP_KERNEL);
-		if (!q->backlogs)
-			return -ENOMEM;
-
+		if (!q->backlogs) {
+			err = -ENOMEM;
+			goto alloc_failure;
+		}
 		for (i = 0; i < q->flows_cnt; i++) {
 			struct fq_codel_flow *flow = q->flows + i;
 
@@ -508,6 +510,13 @@ static int fq_codel_init(struct Qdisc *sch, struct nlattr *opt,
 	else
 		sch->flags &= ~TCQ_F_CAN_BYPASS;
 	return 0;
+
+alloc_failure:
+	kvfree(q->flows);
+	q->flows = NULL;
+init_failure:
+	q->flows_cnt = 0;
+	return err;
 }
 
 static int fq_codel_dump(struct Qdisc *sch, struct sk_buff *skb)