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Message-ID: <69170425.050a0220.3565dc.003e.GAE@google.com>
Date: Fri, 14 Nov 2025 02:27:49 -0800
From: syzbot <syzbot+7902f127c28c701e913f@...kaller.appspotmail.com>
To: matttbe@...nel.org
Cc: davem@...emloft.net, edumazet@...gle.com, geliang@...nel.org,
horms@...nel.org, kuba@...nel.org, linux-kernel@...r.kernel.org,
martineau@...nel.org, matttbe@...nel.org, mptcp@...ts.linux.dev,
netdev@...r.kernel.org, pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mptcp?] possible deadlock in mptcp_subflow_shutdown (2)
> Hello,
>
> On 10/11/2025 09:41, Paolo Abeni wrote:
>> On 11/10/25 2:29 AM, syzbot wrote:
>>> syzbot found the following issue on:
>>>
>>> HEAD commit: dc77806cf3b4 Merge tag 'rust-fixes-6.18' of git://git.kern..
>>> git tree: upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=17dd9bcd980000
>>> kernel config: https://syzkaller.appspot.com/x/.config?x=19d831c6d0386a9c
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=7902f127c28c701e913f
>>> compiler: gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
>>>
>>> Unfortunately, I don't have any reproducer for this issue yet.
>>>
>>> Downloadable assets:
>>> disk image: https://storage.googleapis.com/syzbot-assets/a1c9259ca92c/disk-dc77806c.raw.xz
>>> vmlinux: https://storage.googleapis.com/syzbot-assets/98d084f2ad8b/vmlinux-dc77806c.xz
>>> kernel image: https://storage.googleapis.com/syzbot-assets/c25e628e3491/bzImage-dc77806c.xz
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+7902f127c28c701e913f@...kaller.appspotmail.com
>>>
>>> ======================================================
>>> WARNING: possible circular locking dependency detected
>>> syzkaller #0 Not tainted
>>> ------------------------------------------------------
>>> syz.7.3695/23717 is trying to acquire lock:
>>> ffff888087316860 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1679 [inline]
>>> ffff888087316860 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_subflow_shutdown+0x24/0x380 net/mptcp/protocol.c:2918
>>>
>>> but task is already holding lock:
>>> ffff888026899a60 (sk_lock-AF_INET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1679 [inline]
>>> ffff888026899a60 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_close+0x1d/0xe0 net/mptcp/protocol.c:3168
>>>
>>> which lock already depends on the new lock.
>>>
>>>
>>> the existing dependency chain (in reverse order) is:
>>>
>>> -> #7 (sk_lock-AF_INET){+.+.}-{0:0}:
>>> lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
>>> lock_sock include/net/sock.h:1679 [inline]
>>> inet_shutdown+0x67/0x440 net/ipv4/af_inet.c:907
>>> nbd_mark_nsock_dead+0xae/0x5d0 drivers/block/nbd.c:319
>>> recv_work+0x671/0xa80 drivers/block/nbd.c:1024
>>> process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
>>> process_scheduled_works kernel/workqueue.c:3346 [inline]
>>> worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
>>> kthread+0x3c5/0x780 kernel/kthread.c:463
>>> ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>>>
>>> -> #6 (&nsock->tx_lock){+.+.}-{4:4}:
>>> __mutex_lock_common kernel/locking/mutex.c:598 [inline]
>>> __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
>>> nbd_handle_cmd drivers/block/nbd.c:1146 [inline]
>>> nbd_queue_rq+0x423/0x12d0 drivers/block/nbd.c:1210
>>> blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2129
>>> __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
>>> blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
>>> __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
>>> blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
>>> blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
>>> blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
>>> blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
>>> blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
>>> __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
>>> blk_finish_plug block/blk-core.c:1252 [inline]
>>> blk_finish_plug block/blk-core.c:1249 [inline]
>>> __submit_bio+0x545/0x690 block/blk-core.c:651
>>> __submit_bio_noacct_mq block/blk-core.c:724 [inline]
>>> submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
>>> submit_bio_noacct+0x5bd/0x1f60 block/blk-core.c:879
>>> submit_bh fs/buffer.c:2829 [inline]
>>> block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
>>> filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
>>> do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4024
>>> read_mapping_folio include/linux/pagemap.h:999 [inline]
>>> read_part_sector+0xd4/0x370 block/partitions/core.c:722
>>> adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
>>> check_partition block/partitions/core.c:141 [inline]
>>> blk_add_partitions block/partitions/core.c:589 [inline]
>>> bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
>>> blkdev_get_whole+0x187/0x290 block/bdev.c:748
>>> bdev_open+0x2c7/0xe40 block/bdev.c:957
>>> blkdev_open+0x34e/0x4f0 block/fops.c:701
>>> do_dentry_open+0x982/0x1530 fs/open.c:965
>>> vfs_open+0x82/0x3f0 fs/open.c:1097
>>> do_open fs/namei.c:3975 [inline]
>>> path_openat+0x1de4/0x2cb0 fs/namei.c:4134
>>> do_filp_open+0x20b/0x470 fs/namei.c:4161
>>> do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
>>> do_sys_open fs/open.c:1452 [inline]
>>> __do_sys_openat fs/open.c:1468 [inline]
>>> __se_sys_openat fs/open.c:1463 [inline]
>>> __x64_sys_openat+0x174/0x210 fs/open.c:1463
>>> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>> do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>
>>> -> #5 (&cmd->lock){+.+.}-{4:4}:
>>> __mutex_lock_common kernel/locking/mutex.c:598 [inline]
>>> __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
>>> nbd_queue_rq+0xbd/0x12d0 drivers/block/nbd.c:1202
>>> blk_mq_dispatch_rq_list+0x416/0x1e20 block/blk-mq.c:2129
>>> __blk_mq_do_dispatch_sched block/blk-mq-sched.c:168 [inline]
>>> blk_mq_do_dispatch_sched block/blk-mq-sched.c:182 [inline]
>>> __blk_mq_sched_dispatch_requests+0xcb7/0x15f0 block/blk-mq-sched.c:307
>>> blk_mq_sched_dispatch_requests+0xd8/0x1b0 block/blk-mq-sched.c:329
>>> blk_mq_run_hw_queue+0x239/0x670 block/blk-mq.c:2367
>>> blk_mq_dispatch_list+0x514/0x1310 block/blk-mq.c:2928
>>> blk_mq_flush_plug_list block/blk-mq.c:2976 [inline]
>>> blk_mq_flush_plug_list+0x130/0x600 block/blk-mq.c:2948
>>> __blk_flush_plug+0x2c4/0x4b0 block/blk-core.c:1225
>>> blk_finish_plug block/blk-core.c:1252 [inline]
>>> blk_finish_plug block/blk-core.c:1249 [inline]
>>> __submit_bio+0x545/0x690 block/blk-core.c:651
>>> __submit_bio_noacct_mq block/blk-core.c:724 [inline]
>>> submit_bio_noacct_nocheck+0x53d/0xc10 block/blk-core.c:755
>>> submit_bio_noacct+0x5bd/0x1f60 block/blk-core.c:879
>>> submit_bh fs/buffer.c:2829 [inline]
>>> block_read_full_folio+0x4db/0x850 fs/buffer.c:2461
>>> filemap_read_folio+0xc8/0x2a0 mm/filemap.c:2444
>>> do_read_cache_folio+0x263/0x5c0 mm/filemap.c:4024
>>> read_mapping_folio include/linux/pagemap.h:999 [inline]
>>> read_part_sector+0xd4/0x370 block/partitions/core.c:722
>>> adfspart_check_ICS+0x93/0x940 block/partitions/acorn.c:360
>>> check_partition block/partitions/core.c:141 [inline]
>>> blk_add_partitions block/partitions/core.c:589 [inline]
>>> bdev_disk_changed+0x723/0x1520 block/partitions/core.c:693
>>> blkdev_get_whole+0x187/0x290 block/bdev.c:748
>>> bdev_open+0x2c7/0xe40 block/bdev.c:957
>>> blkdev_open+0x34e/0x4f0 block/fops.c:701
>>> do_dentry_open+0x982/0x1530 fs/open.c:965
>>> vfs_open+0x82/0x3f0 fs/open.c:1097
>>> do_open fs/namei.c:3975 [inline]
>>> path_openat+0x1de4/0x2cb0 fs/namei.c:4134
>>> do_filp_open+0x20b/0x470 fs/namei.c:4161
>>> do_sys_openat2+0x11b/0x1d0 fs/open.c:1437
>>> do_sys_open fs/open.c:1452 [inline]
>>> __do_sys_openat fs/open.c:1468 [inline]
>>> __se_sys_openat fs/open.c:1463 [inline]
>>> __x64_sys_openat+0x174/0x210 fs/open.c:1463
>>> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>> do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>
>>> -> #4 (set->srcu){.+.+}-{0:0}:
>>> srcu_lock_sync include/linux/srcu.h:173 [inline]
>>> __synchronize_srcu+0xa1/0x290 kernel/rcu/srcutree.c:1439
>>> blk_mq_wait_quiesce_done block/blk-mq.c:283 [inline]
>>> blk_mq_wait_quiesce_done block/blk-mq.c:280 [inline]
>>> blk_mq_quiesce_queue block/blk-mq.c:303 [inline]
>>> blk_mq_quiesce_queue+0x149/0x1b0 block/blk-mq.c:298
>>> elevator_switch+0x17d/0x810 block/elevator.c:588
>>> elevator_change+0x391/0x5d0 block/elevator.c:691
>>> elevator_set_default+0x2e9/0x380 block/elevator.c:767
>>> blk_register_queue+0x384/0x4e0 block/blk-sysfs.c:942
>>> __add_disk+0x74a/0xf00 block/genhd.c:528
>>> add_disk_fwnode+0x13f/0x5d0 block/genhd.c:597
>>> add_disk include/linux/blkdev.h:775 [inline]
>>> nbd_dev_add+0x783/0xbb0 drivers/block/nbd.c:1987
>>> nbd_init+0x1a2/0x3c0 drivers/block/nbd.c:2702
>>> do_one_initcall+0x123/0x6e0 init/main.c:1283
>>> do_initcall_level init/main.c:1345 [inline]
>>> do_initcalls init/main.c:1361 [inline]
>>> do_basic_setup init/main.c:1380 [inline]
>>> kernel_init_freeable+0x5c8/0x920 init/main.c:1593
>>> kernel_init+0x1c/0x2b0 init/main.c:1483
>>> ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>>>
>>> -> #3 (&q->elevator_lock){+.+.}-{4:4}:
>>> __mutex_lock_common kernel/locking/mutex.c:598 [inline]
>>> __mutex_lock+0x193/0x1060 kernel/locking/mutex.c:760
>>> queue_requests_store+0x3a7/0x670 block/blk-sysfs.c:117
>>> queue_attr_store+0x26b/0x310 block/blk-sysfs.c:869
>>> sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
>>> kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
>>> new_sync_write fs/read_write.c:593 [inline]
>>> vfs_write+0x7d3/0x11d0 fs/read_write.c:686
>>> ksys_write+0x12a/0x250 fs/read_write.c:738
>>> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>> do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>
>>> -> #2 (&q->q_usage_counter(io)#52){++++}-{0:0}:
>>> blk_alloc_queue+0x619/0x760 block/blk-core.c:461
>>> blk_mq_alloc_queue+0x172/0x280 block/blk-mq.c:4399
>>> __blk_mq_alloc_disk+0x29/0x120 block/blk-mq.c:4446
>>> nbd_dev_add+0x492/0xbb0 drivers/block/nbd.c:1957
>>> nbd_init+0x1a2/0x3c0 drivers/block/nbd.c:2702
>>> do_one_initcall+0x123/0x6e0 init/main.c:1283
>>> do_initcall_level init/main.c:1345 [inline]
>>> do_initcalls init/main.c:1361 [inline]
>>> do_basic_setup init/main.c:1380 [inline]
>>> kernel_init_freeable+0x5c8/0x920 init/main.c:1593
>>> kernel_init+0x1c/0x2b0 init/main.c:1483
>>> ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>>>
>>> -> #1 (fs_reclaim){+.+.}-{0:0}:
>>> __fs_reclaim_acquire mm/page_alloc.c:4269 [inline]
>>> fs_reclaim_acquire+0x102/0x150 mm/page_alloc.c:4283
>>> might_alloc include/linux/sched/mm.h:318 [inline]
>>> slab_pre_alloc_hook mm/slub.c:4921 [inline]
>>> slab_alloc_node mm/slub.c:5256 [inline]
>>> __kmalloc_cache_noprof+0x58/0x780 mm/slub.c:5758
>>> kmalloc_noprof include/linux/slab.h:957 [inline]
>>> kzalloc_noprof include/linux/slab.h:1094 [inline]
>>> ref_tracker_alloc+0x18e/0x5b0 lib/ref_tracker.c:271
>>> __netns_tracker_alloc include/net/net_namespace.h:362 [inline]
>>> netns_tracker_alloc include/net/net_namespace.h:371 [inline]
>>> get_net_track include/net/net_namespace.h:388 [inline]
>>> sk_net_refcnt_upgrade+0x141/0x1e0 net/core/sock.c:2384
>>> rds_tcp_tune+0x23d/0x530 net/rds/tcp.c:507
>>> rds_tcp_conn_path_connect+0x305/0x7f0 net/rds/tcp_connect.c:127
>>> rds_connect_worker+0x1af/0x2c0 net/rds/threads.c:176
>>> process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
>>> process_scheduled_works kernel/workqueue.c:3346 [inline]
>>> worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
>>> kthread+0x3c5/0x780 kernel/kthread.c:463
>>> ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
>>> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>>>
>>> -> #0 (k-sk_lock-AF_INET){+.+.}-{0:0}:
>>> check_prev_add kernel/locking/lockdep.c:3165 [inline]
>>> check_prevs_add kernel/locking/lockdep.c:3284 [inline]
>>> validate_chain kernel/locking/lockdep.c:3908 [inline]
>>> __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5237
>>> lock_acquire kernel/locking/lockdep.c:5868 [inline]
>>> lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
>>> lock_sock_nested+0x41/0xf0 net/core/sock.c:3720
>>> lock_sock include/net/sock.h:1679 [inline]
>>> mptcp_subflow_shutdown+0x24/0x380 net/mptcp/protocol.c:2918
>>> mptcp_check_send_data_fin+0x248/0x440 net/mptcp/protocol.c:3022
>>> __mptcp_close+0x90e/0xbe0 net/mptcp/protocol.c:3116
>>> mptcp_close+0x28/0xe0 net/mptcp/protocol.c:3170
>>> inet_release+0xed/0x200 net/ipv4/af_inet.c:437
>>> __sock_release+0xb3/0x270 net/socket.c:662
>>> sock_close+0x1c/0x30 net/socket.c:1455
>>> __fput+0x402/0xb70 fs/file_table.c:468
>>> task_work_run+0x150/0x240 kernel/task_work.c:227
>>> resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>>> exit_to_user_mode_loop+0xec/0x130 kernel/entry/common.c:43
>>> exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
>>> syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
>>> syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
>>> do_syscall_64+0x426/0xfa0 arch/x86/entry/syscall_64.c:100
>>> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>>
>>> other info that might help us debug this:
>>>
>>> Chain exists of:
>>> k-sk_lock-AF_INET --> &nsock->tx_lock --> sk_lock-AF_INET
>>
>> It looks like a false positive due to mptcp subflows and nbd connection
>> sockets getting the lockdep annotation. We should possibly/likely use a
>> specific lockdep key for mptcp subflows.
>
> As noted by Paolo offline, it looks like this issue is due to nbd
> introducing a lockdep dependency between reclaim and af_socket, and this
> is similar to a previous report:
>
> #syz dup: [syzbot] [mptcp?] possible deadlock in
can't find the dup bug
> mptcp_subflow_create_socket (2)
>
> Cheers,
> Matt
> --
> Sponsored by the NGI0 Core fund.
>
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