netdev - [PATCH net] net: sched: fix warn on htb offloaded class creation

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Date: Thu, 26 Oct 2023 17:36:48 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: netdev@...r.kernel.org
Cc: Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Tariq Toukan <tariqt@...dia.com>,
	Maxim Mikityanskiy <maxtram95@...il.com>
Subject: [PATCH net] net: sched: fix warn on htb offloaded class creation

The following commands:

tc qdisc add dev eth1 handle 2: root htb offload
tc class add dev eth1 parent 2: classid 2:1 htb rate 5mbit burst 15k

yeld to a WARN in the HTB qdisc:

 WARNING: CPU: 2 PID: 1583 at net/sched/sch_htb.c:1959
 CPU: 2 PID: 1583 Comm: tc Kdump: loaded 6.6.0-rc2.mptcp_7895773e5235+ #59
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
 RIP: 0010:htb_change_class+0x25c4/0x2e30 [sch_htb]
 Code: 24 58 48 b8 00 00 00 00 00 fc ff df 48 89 ca 48 c1 ea 03 80 3c 02 00 0f 85 92 01 00 00 49 89 8c 24 b0 01 00 00 e9 77 fc ff ff <0f> 0b e9 15 ec ff ff 80 3d f8 35 00 00 00 0f 85 d4 f9 ff ff ba 32
 RSP: 0018:ffffc900015df240 EFLAGS: 00010246
 RAX: 0000000000000000 RBX: ffff88811b4ca000 RCX: ffff88811db42800
 RDX: 1ffff11023b68502 RSI: ffffffffaf2e6a00 RDI: ffff88811db42810
 RBP: ffff88811db45000 R08: 0000000000000001 R09: fffffbfff664bbc9
 R10: ffffffffb325de4f R11: ffffffffb2d33748 R12: 0000000000000000
 R13: ffff88811db43000 R14: ffff88811b4caaac R15: ffff8881252c0030
 FS:  00007f6c1f126740(0000) GS:ffff88815aa00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 000055dca8e5b4a8 CR3: 000000011bc7a006 CR4: 0000000000370ee0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
 Call Trace:
 <TASK>
  tc_ctl_tclass+0x394/0xeb0
  rtnetlink_rcv_msg+0x2f5/0xaa0
  netlink_rcv_skb+0x12e/0x3a0
  netlink_unicast+0x421/0x730
  netlink_sendmsg+0x79e/0xc60
  ____sys_sendmsg+0x95a/0xc20
  ___sys_sendmsg+0xee/0x170
  __sys_sendmsg+0xc6/0x170
 do_syscall_64+0x58/0x80
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8

The first command creates per TX queue pfifo qdiscs in
tc_modify_qdisc() -> htb_init() and grafts the pfifo to each dev_queue
via tc_modify_qdisc() ->  qdisc_graft() -> htb_attach().

When the command completes, the qdisc_sleeping for each dev_queue is a
pfifo one. The next class creation will trigger the reported splat.

Address the issue taking care of old non-builtin qdisc in
htb_change_class().

Fixes: d03b195b5aa0 ("sch_htb: Hierarchical QoS hardware offload")
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/sched/sch_htb.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c
index 0d947414e616..dc682bd542b4 100644
--- a/net/sched/sch_htb.c
+++ b/net/sched/sch_htb.c
@@ -1955,8 +1955,7 @@ static int htb_change_class(struct Qdisc *sch, u32 classid,
 				qdisc_refcount_inc(new_q);
 			}
 			old_q = htb_graft_helper(dev_queue, new_q);
-			/* No qdisc_put needed. */
-			WARN_ON(!(old_q->flags & TCQ_F_BUILTIN));
+			qdisc_put(old_q);
 		}
 		sch_tree_lock(sch);
 		if (parent && !parent->level) {
-- 
2.41.0