From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 83F5BC4332F for ; Thu, 3 Nov 2022 16:32:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231910AbiKCQbz (ORCPT ); Thu, 3 Nov 2022 12:31:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55484 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232100AbiKCQba (ORCPT ); Thu, 3 Nov 2022 12:31:30 -0400 Received: from mail-ej1-x630.google.com (mail-ej1-x630.google.com [IPv6:2a00:1450:4864:20::630]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 909511C92C for ; Thu, 3 Nov 2022 09:31:15 -0700 (PDT) Received: by mail-ej1-x630.google.com with SMTP id bj12so6666064ejb.13 for ; Thu, 03 Nov 2022 09:31:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=DHG6rl/QgfxaB7eq3Wx455iWSDI12emRLZZsK8iZ76E=; b=fPZCcWv8VVgpaHw8B2X0DJmWvjYB7lJhn4ofbFFmNf76Ns3Y60bDIcLOfQBPJMHMSV 7dRr4z81yCRGRCqgeDVA5WUMCYdTcsjh+D1WUhMQuC4DUWsf3aW1m/S/fl8eAfjW9JkB 2em2TIAvUQTfwPrSFXzwKfiKnOQmQ5/SmLcko+9JrtC/qSfcPUpk2rk8WI73tqBUr8/y Oes8p3b3dd43NkPpNWQp89iZ4Ks3qdSDpy4R5n6hOR9QWxNKAgIyo3w+I7XgiHwOpvEn WwlVfdVAFukPogG1vwqnKXWwIthgAQGwY8DbEBQfa2dlhfuUbTOKT9U2Iyl3B3mde/7Y ZVEQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=DHG6rl/QgfxaB7eq3Wx455iWSDI12emRLZZsK8iZ76E=; b=twa+h9Z2IS8TKQvFRMM8FADoS0jFG/gVgZY1I/jNxJ5nWN8uN4bQDjVzoXfluKi13I nW44hWS57jx3KM+CDyZkGHp+ZDeuqFY6eBR0A7GCMyBKUv5Pc5SFDC1U8bvzslExgL5F ySutA3Dp79s5HGqF5TEyqkgy4gyV1sf47bE/4qCgRzp7tOJns9Ytzubjg9CPnTtYjxR6 ueMSOrFoUoQgronlrm+0uW5p/Ba3CQcv088hM9ht87puk+8TrkH755uzjDNxBODZf8vU V1pUzpqXCYC7YpNJF2KSfES1GrwQeIKfp7zvr5vvcrdVf6VUGITGqqYCa1GXZs9K2VIx ufBg== X-Gm-Message-State: ACrzQf3UsZRRnJtefAJISayKXulPX+fRcHrkSs100rQQBtulVbKL5DsL PhR6BqgEPr0RTPrYu+4HsLoTHcq5RO8HNP5IRac= X-Google-Smtp-Source: AMsMyM6Tqql2ZoaHRIOXNtkHRSyJZH9Uk7xVhtQZ//9yFX3D02oY1wlwbwNL5TsXoIABNbKxS3hI3eYUn65I5DLaMPU= X-Received: by 2002:a17:907:9495:b0:78e:1bee:5919 with SMTP id dm21-20020a170907949500b0078e1bee5919mr29826981ejc.701.1667493073984; Thu, 03 Nov 2022 09:31:13 -0700 (PDT) MIME-Version: 1.0 References: <20221018203258.2793282-1-edumazet@google.com> <162f9155-dfe3-9d78-c59f-f47f7dcf83f5@nvidia.com> <20221103082751.353faa4d@kernel.org> In-Reply-To: From: Maxim Mikityanskiy Date: Thu, 3 Nov 2022 18:30:47 +0200 Message-ID: Subject: Re: [PATCH net] net: sched: fix race condition in qdisc_graft() To: Eric Dumazet Cc: Jakub Kicinski , Gal Pressman , Maxim Mikityanskiy , "David S . Miller" , Paolo Abeni , netdev@vger.kernel.org, Cong Wang , eric.dumazet@gmail.com, syzbot , Dmitry Vyukov , Tariq Toukan Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, 3 Nov 2022 at 17:30, Eric Dumazet wrote: > > On Thu, Nov 3, 2022 at 8:27 AM Jakub Kicinski wrote: > > > > On Thu, 3 Nov 2022 08:17:06 -0700 Eric Dumazet wrote: > > > On Thu, Nov 3, 2022 at 6:34 AM Gal Pressman wrote: > > > > > > > > On 18/10/2022 23:32, Eric Dumazet wrote: > > > > > We had one syzbot report [1] in syzbot queue for a while. > > > > > I was waiting for more occurrences and/or a repro but > > > > > Dmitry Vyukov spotted the issue right away. > > > > > > > > > > > > > > > qdisc_graft() drops reference to qdisc in notify_and_destroy > > > > > while it's still assigned to dev->qdisc > > > > > > > > > > > > > > > Indeed, RCU rules are clear when replacing a data structure. > > > > > The visible pointer (dev->qdisc in this case) must be updated > > > > > to the new object _before_ RCU grace period is started > > > > > (qdisc_put(old) in this case). > > > > > > > > > > [1] > > > > > BUG: KASAN: use-after-free in __tcf_qdisc_find.part.0+0xa3a/0xac0 net/sched/cls_api.c:1066 > > > > > Read of size 4 at addr ffff88802065e038 by task syz-executor.4/21027 > > > > > > > > > > CPU: 0 PID: 21027 Comm: syz-executor.4 Not tainted 6.0.0-rc3-syzkaller-00363-g7726d4c3e60b #0 > > > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2022 > > > > > Call Trace: > > > > > > > > > > __dump_stack lib/dump_stack.c:88 [inline] > > > > > dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 > > > > > print_address_description mm/kasan/report.c:317 [inline] > > > > > print_report.cold+0x2ba/0x719 mm/kasan/report.c:433 > > > > > kasan_report+0xb1/0x1e0 mm/kasan/report.c:495 > > > > > __tcf_qdisc_find.part.0+0xa3a/0xac0 net/sched/cls_api.c:1066 > > > > > __tcf_qdisc_find net/sched/cls_api.c:1051 [inline] > > > > > tc_new_tfilter+0x34f/0x2200 net/sched/cls_api.c:2018 > > > > > rtnetlink_rcv_msg+0x955/0xca0 net/core/rtnetlink.c:6081 > > > > > netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501 > > > > > netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] > > > > > netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345 > > > > > netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921 > > > > > sock_sendmsg_nosec net/socket.c:714 [inline] > > > > > sock_sendmsg+0xcf/0x120 net/socket.c:734 > > > > > ____sys_sendmsg+0x6eb/0x810 net/socket.c:2482 > > > > > ___sys_sendmsg+0x110/0x1b0 net/socket.c:2536 > > > > > __sys_sendmsg+0xf3/0x1c0 net/socket.c:2565 > > > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > RIP: 0033:0x7f5efaa89279 > > > > > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 > > > > > RSP: 002b:00007f5efbc31168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e > > > > > RAX: ffffffffffffffda RBX: 00007f5efab9bf80 RCX: 00007f5efaa89279 > > > > > RDX: 0000000000000000 RSI: 0000000020000140 RDI: 0000000000000005 > > > > > RBP: 00007f5efaae32e9 R08: 0000000000000000 R09: 0000000000000000 > > > > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > > > > R13: 00007f5efb0cfb1f R14: 00007f5efbc31300 R15: 0000000000022000 > > > > > > > > > > > > > > > Allocated by task 21027: > > > > > kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38 > > > > > kasan_set_track mm/kasan/common.c:45 [inline] > > > > > set_alloc_info mm/kasan/common.c:437 [inline] > > > > > ____kasan_kmalloc mm/kasan/common.c:516 [inline] > > > > > ____kasan_kmalloc mm/kasan/common.c:475 [inline] > > > > > __kasan_kmalloc+0xa9/0xd0 mm/kasan/common.c:525 > > > > > kmalloc_node include/linux/slab.h:623 [inline] > > > > > kzalloc_node include/linux/slab.h:744 [inline] > > > > > qdisc_alloc+0xb0/0xc50 net/sched/sch_generic.c:938 > > > > > qdisc_create_dflt+0x71/0x4a0 net/sched/sch_generic.c:997 > > > > > attach_one_default_qdisc net/sched/sch_generic.c:1152 [inline] > > > > > netdev_for_each_tx_queue include/linux/netdevice.h:2437 [inline] > > > > > attach_default_qdiscs net/sched/sch_generic.c:1170 [inline] > > > > > dev_activate+0x760/0xcd0 net/sched/sch_generic.c:1229 > > > > > __dev_open+0x393/0x4d0 net/core/dev.c:1441 > > > > > __dev_change_flags+0x583/0x750 net/core/dev.c:8556 > > > > > rtnl_configure_link+0xee/0x240 net/core/rtnetlink.c:3189 > > > > > rtnl_newlink_create net/core/rtnetlink.c:3371 [inline] > > > > > __rtnl_newlink+0x10b8/0x17e0 net/core/rtnetlink.c:3580 > > > > > rtnl_newlink+0x64/0xa0 net/core/rtnetlink.c:3593 > > > > > rtnetlink_rcv_msg+0x43a/0xca0 net/core/rtnetlink.c:6090 > > > > > netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501 > > > > > netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] > > > > > netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345 > > > > > netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921 > > > > > sock_sendmsg_nosec net/socket.c:714 [inline] > > > > > sock_sendmsg+0xcf/0x120 net/socket.c:734 > > > > > ____sys_sendmsg+0x6eb/0x810 net/socket.c:2482 > > > > > ___sys_sendmsg+0x110/0x1b0 net/socket.c:2536 > > > > > __sys_sendmsg+0xf3/0x1c0 net/socket.c:2565 > > > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > > > > > Freed by task 21020: > > > > > kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38 > > > > > kasan_set_track+0x21/0x30 mm/kasan/common.c:45 > > > > > kasan_set_free_info+0x20/0x30 mm/kasan/generic.c:370 > > > > > ____kasan_slab_free mm/kasan/common.c:367 [inline] > > > > > ____kasan_slab_free+0x166/0x1c0 mm/kasan/common.c:329 > > > > > kasan_slab_free include/linux/kasan.h:200 [inline] > > > > > slab_free_hook mm/slub.c:1754 [inline] > > > > > slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1780 > > > > > slab_free mm/slub.c:3534 [inline] > > > > > kfree+0xe2/0x580 mm/slub.c:4562 > > > > > rcu_do_batch kernel/rcu/tree.c:2245 [inline] > > > > > rcu_core+0x7b5/0x1890 kernel/rcu/tree.c:2505 > > > > > __do_softirq+0x1d3/0x9c6 kernel/softirq.c:571 > > > > > > > > > > Last potentially related work creation: > > > > > kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38 > > > > > __kasan_record_aux_stack+0xbe/0xd0 mm/kasan/generic.c:348 > > > > > call_rcu+0x99/0x790 kernel/rcu/tree.c:2793 > > > > > qdisc_put+0xcd/0xe0 net/sched/sch_generic.c:1083 > > > > > notify_and_destroy net/sched/sch_api.c:1012 [inline] > > > > > qdisc_graft+0xeb1/0x1270 net/sched/sch_api.c:1084 > > > > > tc_modify_qdisc+0xbb7/0x1a00 net/sched/sch_api.c:1671 > > > > > rtnetlink_rcv_msg+0x43a/0xca0 net/core/rtnetlink.c:6090 > > > > > netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2501 > > > > > netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline] > > > > > netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345 > > > > > netlink_sendmsg+0x917/0xe10 net/netlink/af_netlink.c:1921 > > > > > sock_sendmsg_nosec net/socket.c:714 [inline] > > > > > sock_sendmsg+0xcf/0x120 net/socket.c:734 > > > > > ____sys_sendmsg+0x6eb/0x810 net/socket.c:2482 > > > > > ___sys_sendmsg+0x110/0x1b0 net/socket.c:2536 > > > > > __sys_sendmsg+0xf3/0x1c0 net/socket.c:2565 > > > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > > > > > Second to last potentially related work creation: > > > > > kasan_save_stack+0x1e/0x40 mm/kasan/common.c:38 > > > > > __kasan_record_aux_stack+0xbe/0xd0 mm/kasan/generic.c:348 > > > > > kvfree_call_rcu+0x74/0x940 kernel/rcu/tree.c:3322 > > > > > neigh_destroy+0x431/0x630 net/core/neighbour.c:912 > > > > > neigh_release include/net/neighbour.h:454 [inline] > > > > > neigh_cleanup_and_release+0x1f8/0x330 net/core/neighbour.c:103 > > > > > neigh_del net/core/neighbour.c:225 [inline] > > > > > neigh_remove_one+0x37d/0x460 net/core/neighbour.c:246 > > > > > neigh_forced_gc net/core/neighbour.c:276 [inline] > > > > > neigh_alloc net/core/neighbour.c:447 [inline] > > > > > ___neigh_create+0x18b5/0x29a0 net/core/neighbour.c:642 > > > > > ip6_finish_output2+0xfb8/0x1520 net/ipv6/ip6_output.c:125 > > > > > __ip6_finish_output net/ipv6/ip6_output.c:195 [inline] > > > > > ip6_finish_output+0x690/0x1160 net/ipv6/ip6_output.c:206 > > > > > NF_HOOK_COND include/linux/netfilter.h:296 [inline] > > > > > ip6_output+0x1ed/0x540 net/ipv6/ip6_output.c:227 > > > > > dst_output include/net/dst.h:451 [inline] > > > > > NF_HOOK include/linux/netfilter.h:307 [inline] > > > > > NF_HOOK include/linux/netfilter.h:301 [inline] > > > > > mld_sendpack+0xa09/0xe70 net/ipv6/mcast.c:1820 > > > > > mld_send_cr net/ipv6/mcast.c:2121 [inline] > > > > > mld_ifc_work+0x71c/0xdc0 net/ipv6/mcast.c:2653 > > > > > process_one_work+0x991/0x1610 kernel/workqueue.c:2289 > > > > > worker_thread+0x665/0x1080 kernel/workqueue.c:2436 > > > > > kthread+0x2e4/0x3a0 kernel/kthread.c:376 > > > > > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306 > > > > > > > > > > The buggy address belongs to the object at ffff88802065e000 > > > > > which belongs to the cache kmalloc-1k of size 1024 > > > > > The buggy address is located 56 bytes inside of > > > > > 1024-byte region [ffff88802065e000, ffff88802065e400) > > > > > > > > > > The buggy address belongs to the physical page: > > > > > page:ffffea0000819600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x20658 > > > > > head:ffffea0000819600 order:3 compound_mapcount:0 compound_pincount:0 > > > > > flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff) > > > > > raw: 00fff00000010200 0000000000000000 dead000000000001 ffff888011841dc0 > > > > > raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000 > > > > > page dumped because: kasan: bad access detected > > > > > page_owner tracks the page as allocated > > > > > page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 3523, tgid 3523 (sshd), ts 41495190986, free_ts 41417713212 > > > > > prep_new_page mm/page_alloc.c:2532 [inline] > > > > > get_page_from_freelist+0x109b/0x2ce0 mm/page_alloc.c:4283 > > > > > __alloc_pages+0x1c7/0x510 mm/page_alloc.c:5515 > > > > > alloc_pages+0x1a6/0x270 mm/mempolicy.c:2270 > > > > > alloc_slab_page mm/slub.c:1824 [inline] > > > > > allocate_slab+0x27e/0x3d0 mm/slub.c:1969 > > > > > new_slab mm/slub.c:2029 [inline] > > > > > ___slab_alloc+0x7f1/0xe10 mm/slub.c:3031 > > > > > __slab_alloc.constprop.0+0x4d/0xa0 mm/slub.c:3118 > > > > > slab_alloc_node mm/slub.c:3209 [inline] > > > > > __kmalloc_node_track_caller+0x2f2/0x380 mm/slub.c:4955 > > > > > kmalloc_reserve net/core/skbuff.c:358 [inline] > > > > > __alloc_skb+0xd9/0x2f0 net/core/skbuff.c:430 > > > > > alloc_skb_fclone include/linux/skbuff.h:1307 [inline] > > > > > tcp_stream_alloc_skb+0x38/0x580 net/ipv4/tcp.c:861 > > > > > tcp_sendmsg_locked+0xc36/0x2f80 net/ipv4/tcp.c:1325 > > > > > tcp_sendmsg+0x2b/0x40 net/ipv4/tcp.c:1483 > > > > > inet_sendmsg+0x99/0xe0 net/ipv4/af_inet.c:819 > > > > > sock_sendmsg_nosec net/socket.c:714 [inline] > > > > > sock_sendmsg+0xcf/0x120 net/socket.c:734 > > > > > sock_write_iter+0x291/0x3d0 net/socket.c:1108 > > > > > call_write_iter include/linux/fs.h:2187 [inline] > > > > > new_sync_write fs/read_write.c:491 [inline] > > > > > vfs_write+0x9e9/0xdd0 fs/read_write.c:578 > > > > > ksys_write+0x1e8/0x250 fs/read_write.c:631 > > > > > page last free stack trace: > > > > > reset_page_owner include/linux/page_owner.h:24 [inline] > > > > > free_pages_prepare mm/page_alloc.c:1449 [inline] > > > > > free_pcp_prepare+0x5e4/0xd20 mm/page_alloc.c:1499 > > > > > free_unref_page_prepare mm/page_alloc.c:3380 [inline] > > > > > free_unref_page+0x19/0x4d0 mm/page_alloc.c:3476 > > > > > __unfreeze_partials+0x17c/0x1a0 mm/slub.c:2548 > > > > > qlink_free mm/kasan/quarantine.c:168 [inline] > > > > > qlist_free_all+0x6a/0x170 mm/kasan/quarantine.c:187 > > > > > kasan_quarantine_reduce+0x180/0x200 mm/kasan/quarantine.c:294 > > > > > __kasan_slab_alloc+0xa2/0xc0 mm/kasan/common.c:447 > > > > > kasan_slab_alloc include/linux/kasan.h:224 [inline] > > > > > slab_post_alloc_hook mm/slab.h:727 [inline] > > > > > slab_alloc_node mm/slub.c:3243 [inline] > > > > > slab_alloc mm/slub.c:3251 [inline] > > > > > __kmem_cache_alloc_lru mm/slub.c:3258 [inline] > > > > > kmem_cache_alloc+0x267/0x3b0 mm/slub.c:3268 > > > > > kmem_cache_zalloc include/linux/slab.h:723 [inline] > > > > > alloc_buffer_head+0x20/0x140 fs/buffer.c:2974 > > > > > alloc_page_buffers+0x280/0x790 fs/buffer.c:829 > > > > > create_empty_buffers+0x2c/0xee0 fs/buffer.c:1558 > > > > > ext4_block_write_begin+0x1004/0x1530 fs/ext4/inode.c:1074 > > > > > ext4_da_write_begin+0x422/0xae0 fs/ext4/inode.c:2996 > > > > > generic_perform_write+0x246/0x560 mm/filemap.c:3738 > > > > > ext4_buffered_write_iter+0x15b/0x460 fs/ext4/file.c:270 > > > > > ext4_file_write_iter+0x44a/0x1660 fs/ext4/file.c:679 > > > > > call_write_iter include/linux/fs.h:2187 [inline] > > > > > new_sync_write fs/read_write.c:491 [inline] > > > > > vfs_write+0x9e9/0xdd0 fs/read_write.c:578 > > > > > > > > > > Fixes: af356afa010f ("net_sched: reintroduce dev->qdisc for use by sch_api") > > > > > Reported-by: syzbot > > > > > Diagnosed-by: Dmitry Vyukov > > > > > Signed-off-by: Eric Dumazet > > > > > --- > > > > > net/sched/sch_api.c | 5 +++-- > > > > > 1 file changed, 3 insertions(+), 2 deletions(-) > > > > > > > > > > diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c > > > > > index c98af0ada706efee202a20a6bfb6f2b984106f45..4a27dfb1ba0faab3692a82969fb8b78768742779 100644 > > > > > --- a/net/sched/sch_api.c > > > > > +++ b/net/sched/sch_api.c > > > > > @@ -1099,12 +1099,13 @@ static int qdisc_graft(struct net_device *dev, struct Qdisc *parent, > > > > > > > > > > skip: > > > > > if (!ingress) { > > > > > - notify_and_destroy(net, skb, n, classid, > > > > > - rtnl_dereference(dev->qdisc), new); > > > > > + old = rtnl_dereference(dev->qdisc); > > > > > if (new && !new->ops->attach) > > > > > qdisc_refcount_inc(new); > > > > > rcu_assign_pointer(dev->qdisc, new ? : &noop_qdisc); > > > > > > > > > > + notify_and_destroy(net, skb, n, classid, old, new); > > > > > + > > > > > if (new && new->ops->attach) > > > > > new->ops->attach(new); > > > > > } else { > > > > > > > > Hi Eric, > > > > We started seeing the following WARN_ON happening on htb destroy > > > > following your patch: > > > > https://elixir.bootlin.com/linux/v6.1-rc3/source/net/sched/sch_htb.c#L1561 > > > > > > > > Anything comes to mind? > > > > > > Not really. Let's ask Maxim Mikityanskiy > > > > CC: Maxim on non-nvidia address > > > > > Wild guess is that we need this fix: > > diff --git a/net/sched/sch_htb.c b/net/sched/sch_htb.c > index e5b4bbf3ce3d5f36edb512d4017ebd97209bb377..f82c07bd3d60e26e5a1fe2b335dbec29aebb602e > 100644 > --- a/net/sched/sch_htb.c > +++ b/net/sched/sch_htb.c > @@ -1558,7 +1558,7 @@ static int htb_destroy_class_offload(struct > Qdisc *sch, struct htb_class *cl, > /* Before HTB is destroyed, the kernel grafts noop_qdisc to > * all queues. > */ > - WARN_ON(!(old->flags & TCQ_F_BUILTIN)); > + WARN_ON(old && !(old->flags & TCQ_F_BUILTIN)); I don't think it's the right fix. If the WARN_ON happens and doesn't complain about old == NULL, it's not NULL, so this extra check won't help. In any case, old comes from dev_graft_qdisc, which should never return NULL. Maybe something changed after Eric's patch, so that the statement above is no longer true? I.e. I expect a noop_qdisc here, but there is some other qdisc attached to the queue. I need to recall what was the destroy flow and what code assigned noop_qdisc there... > else > WARN_ON(old != q); > > > > > > I can provide the exact shell commands and more info if needed. > > > > > > > > Thanks > >