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AKwUvBx8m2sBQUqmQRBzVWTb6tUrODRzJXwd69xs2oqi/MEDcz5oA1+apei3/OeNdp2op2NUGiu7C9A=@vger.kernel.org X-Gm-Message-State: AFuF++ksOay3kyluinD4pV8Ft6c7g7of4rbjDbATNtVFAqg+cp9RuCpc Y4DXb+tAghZ54rURBs+15673ibsk6v9WP4sN5VJU3SctwrRq9jUw8Ek4kUK7FNaddsl39POUt3J KprRg3D9sjxZs/ran9RoWZ/2trSQk6DeHTyxnlcEl7lMAlZd0/HoFv8op4Zc= Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Received: by 2002:a05:6808:4fc7:b0:4d6:9153:296a with SMTP id 5614622812f47-4d72b93ddf9mr1428058b6e.59.1790217604658; Wed, 23 Sep 2026 19:40:04 -0700 (PDT) Date: Wed, 23 Sep 2026 19:40:04 -0700 In-Reply-To: <20260921190452.1467853-1-kuba@kernel.org> X-Google-Appengine-App-Id: s~syzkaller X-Google-Appengine-App-Id-Alias: syzkaller Message-ID: <6ab48d84.80e1c6cc.1e8e5f.0008.GAE@google.com> Subject: [syzbot ci] Re: net: opt loopback into instance locking From: syzbot ci To: andrew@lunn.ch, davem@davemloft.net, edumazet@google.com, horms@kernel.org, kuba@kernel.org, netdev@vger.kernel.org, pabeni@redhat.com Cc: syzbot@lists.linux.dev, syzkaller-bugs@googlegroups.com Content-Type: text/plain; charset="UTF-8" syzbot ci has tested the following series [v2] net: opt loopback into instance locking https://lore.kernel.org/all/20260921190452.1467853-1-kuba@kernel.org * [PATCH net-next v2] net: opt loopback into instance locking and found the following issue: possible deadlock in default_device_exit_batch Full report is available here: https://ci.syzbot.org/series/23f51d46-5d1a-4839-a0a8-35d88361ffdb *** possible deadlock in default_device_exit_batch tree: net-next URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/netdev/net-next.git base: 944ae66642b726bd6b25ae71b1e9ff88a0e0bdb0 arch: amd64 compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 config: https://ci.syzbot.org/builds/014063b0-7001-43f1-aa04-57649607febc/config batman_adv: batadv0: Removing interface: batadv_slave_0 batman_adv: batadv0: Removing interface: batadv_slave_1 ====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/u8:3/5652 is trying to acquire lock: ffff88811671ae70 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: unregister_netdevice_many_notify+0x5bb/0x2140 but task is already holding lock: ffff88816d8dae70 (&dev_instance_lock_key){+.+.}-{4:4}, at: unregister_netdevice_many_notify+0x5bb/0x2140 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (&dev_instance_lock_key){+.+.}-{4:4}: __mutex_lock+0x19d/0x1550 unregister_netdevice_many_notify+0x5bb/0x2140 default_device_exit_batch+0x6d4/0x760 ops_undo_list+0x4b4/0x8d0 cleanup_net+0x572/0x810 process_scheduled_works+0xc3d/0x1630 worker_thread+0xa47/0xfb0 kthread+0x38b/0x480 ret_from_fork+0x514/0xb70 ret_from_fork_asm+0x1a/0x30 -> #0 (&dev_instance_lock_key#3){+.+.}-{4:4}: __lock_acquire+0x164c/0x2de0 lock_acquire+0x115/0x350 __mutex_lock+0x19d/0x1550 unregister_netdevice_many_notify+0x5bb/0x2140 default_device_exit_batch+0x6d4/0x760 ops_undo_list+0x4b4/0x8d0 cleanup_net+0x572/0x810 process_scheduled_works+0xc3d/0x1630 worker_thread+0xa47/0xfb0 kthread+0x38b/0x480 ret_from_fork+0x514/0xb70 ret_from_fork_asm+0x1a/0x30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&dev_instance_lock_key); lock(&dev_instance_lock_key#3); lock(&dev_instance_lock_key); lock(&dev_instance_lock_key#3); *** DEADLOCK *** locks held by kworker/u8:3/5652: 6, last CPU#1: #0: ffff8881012d5940 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #1: ffffc9000481fc40 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630 #2: ffffffff90244f08 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xf5/0x810 #3: ffffffff90253760 (rtnl_mutex){+.+.}-{4:4}, at: default_device_exit_batch+0xd0/0x760 #4: ffff888120c40e70 (&dev_instance_lock_key#3){+.+.}-{4:4}, at: unregister_netdevice_many_notify+0x5bb/0x2140 #5: ffff88816d8dae70 (&dev_instance_lock_key){+.+.}-{4:4}, at: unregister_netdevice_many_notify+0x5bb/0x2140 stack backtrace: CPU: 1 UID: 0 PID: 5652 Comm: kworker/u8:3 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014 Workqueue: netns cleanup_net Call Trace: dump_stack_lvl+0xe8/0x150 print_circular_bug+0x2e2/0x300 check_noncircular+0x12f/0x150 __lock_acquire+0x164c/0x2de0 lock_acquire+0x115/0x350 __mutex_lock+0x19d/0x1550 unregister_netdevice_many_notify+0x5bb/0x2140 default_device_exit_batch+0x6d4/0x760 ops_undo_list+0x4b4/0x8d0 cleanup_net+0x572/0x810 process_scheduled_works+0xc3d/0x1630 worker_thread+0xa47/0xfb0 kthread+0x38b/0x480 ret_from_fork+0x514/0xb70 ret_from_fork_asm+0x1a/0x30 *** If these findings have caused you to resend the series or submit a separate fix, please add the following tag to your commit message: Tested-by: syzbot@syzkaller.appspotmail.com --- This report is generated by a bot. It may contain errors. syzbot ci engineers can be reached at syzkaller@googlegroups.com. To test a fix for this bug, please reply with `#syz test` (on a separate line) and attach the patch to the email. Notes: - The patch will be applied on top of the tested series (as an incremental fix). - To test a new version of the whole series, please send it directly to syzbot@lists.linux.dev. - Arguments like custom git repos and branches are not supported.