syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L     
------------------------------------------------------
syz.5.3982/21304 is trying to acquire lock:
ffffffff8f400ec0 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217

but task is already holding lock:
ffff88801129a858 (&pipe->mutex){+.+.}-{4:4}, at: splice_to_socket+0x15f/0x11f0 fs/splice.c:805

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #7 (&pipe->mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       iter_file_splice_write+0x1f3/0x10f0 fs/splice.c:682
       do_splice_from fs/splice.c:936 [inline]
       do_splice+0xef8/0x1940 fs/splice.c:1349
       __do_splice fs/splice.c:1431 [inline]
       __do_sys_splice fs/splice.c:1634 [inline]
       __se_sys_splice+0x353/0x490 fs/splice.c:1616
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #6 (sb_writers#5){.+.+}-{0:0}:
       percpu_down_read_internal include/linux/percpu-rwsem.h:53 [inline]
       percpu_down_read_freezable include/linux/percpu-rwsem.h:83 [inline]
       __sb_start_write include/linux/fs/super.h:19 [inline]
       sb_start_write include/linux/fs/super.h:125 [inline]
       kiocb_start_write include/linux/fs.h:2767 [inline]
       lo_rw_aio+0xb1b/0xf00 drivers/block/loop.c:401
       do_req_filebacked drivers/block/loop.c:433 [inline]
       loop_handle_cmd drivers/block/loop.c:1941 [inline]
       loop_process_work+0x637/0x11b0 drivers/block/loop.c:1976
       process_one_work+0x98b/0x1630 kernel/workqueue.c:3318
       process_scheduled_works kernel/workqueue.c:3401 [inline]
       worker_thread+0xb49/0x1140 kernel/workqueue.c:3482
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #5 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}:
       process_one_work+0x8d7/0x1630 kernel/workqueue.c:3294
       process_scheduled_works kernel/workqueue.c:3401 [inline]
       worker_thread+0xb49/0x1140 kernel/workqueue.c:3482
       kthread+0x388/0x470 kernel/kthread.c:436
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #4 ((wq_completion)loop2){+.+.}-{0:0}:
       touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:4033
       __flush_workqueue+0x14b/0x14f0 kernel/workqueue.c:4075
       drain_workqueue+0xd3/0x390 kernel/workqueue.c:4239
       __loop_clr_fd drivers/block/loop.c:1130 [inline]
       lo_release+0x287/0x8f0 drivers/block/loop.c:1767
       bdev_release+0x541/0x660 block/bdev.c:-1
       blkdev_release+0x15/0x20 block/fops.c:681
       __fput+0x461/0xa70 fs/file_table.c:510
       fput_close_sync+0x11f/0x240 fs/file_table.c:615
       __do_sys_close fs/open.c:1511 [inline]
       __se_sys_close fs/open.c:1496 [inline]
       __x64_sys_close+0x7e/0x110 fs/open.c:1496
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #3 (&disk->open_mutex#4){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       __del_gendisk+0x127/0x980 block/genhd.c:710
       del_gendisk+0xe7/0x160 block/genhd.c:823
       loop_remove+0x42/0xc0 drivers/block/loop.c:2136
       loop_control_remove drivers/block/loop.c:2195 [inline]
       loop_control_ioctl+0x4ba/0x5b0 drivers/block/loop.c:2237
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xff/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
       down_write+0x3a/0x50 kernel/locking/rwsem.c:1625
       blk_mq_update_nr_hw_queues+0xbf/0x1a80 block/blk-mq.c:5242
       nbd_start_device+0x17f/0xb20 drivers/block/nbd.c:1489
       nbd_genl_connect+0x1651/0x1c80 drivers/block/nbd.c:2239
       genl_family_rcv_msg_doit+0x22a/0x330 net/netlink/genetlink.c:1114
       genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
       genl_rcv_msg+0x61c/0x7a0 net/netlink/genetlink.c:1209
       netlink_rcv_skb+0x232/0x4b0 net/netlink/af_netlink.c:2556
       genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x780/0x920 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec+0x13a/0x180 net/socket.c:797
       __sock_sendmsg net/socket.c:812 [inline]
       ____sys_sendmsg+0x55c/0x870 net/socket.c:2716
       ___sys_sendmsg+0x2a5/0x360 net/socket.c:2770
       __sys_sendmsg net/socket.c:2802 [inline]
       __do_sys_sendmsg net/socket.c:2807 [inline]
       __se_sys_sendmsg net/socket.c:2805 [inline]
       __x64_sys_sendmsg+0x1c3/0x2a0 net/socket.c:2805
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (genl_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/rtmutex_api.c:559 [inline]
       mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:578
       genl_lock net/netlink/genetlink.c:35 [inline]
       genl_lock_all net/netlink/genetlink.c:48 [inline]
       genl_register_family+0x7b9/0x17b0 net/netlink/genetlink.c:784
       vdpa_init+0x39/0x70 drivers/vdpa/vdpa.c:1565
       do_one_initcall+0x250/0x870 init/main.c:1347
       do_initcall_level+0x104/0x190 init/main.c:1409
       do_initcalls+0x59/0xa0 init/main.c:1425
       kernel_init_freeable+0x2a6/0x3e0 init/main.c:1658
       kernel_init+0x1d/0x1d0 init/main.c:1548
       ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

-> #0 (cb_lock){++++}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3167 [inline]
       check_prevs_add kernel/locking/lockdep.c:3286 [inline]
       validate_chain kernel/locking/lockdep.c:3910 [inline]
       __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
       down_read+0x97/0x200 kernel/locking/rwsem.c:1568
       genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
       netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
       netlink_unicast+0x780/0x920 net/netlink/af_netlink.c:1345
       netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
       sock_sendmsg_nosec+0x13a/0x180 net/socket.c:797
       __sock_sendmsg net/socket.c:812 [inline]
       sock_sendmsg+0x1ca/0x2d0 net/socket.c:835
       splice_to_socket+0xae5/0x11f0 fs/splice.c:884
       do_splice_from fs/splice.c:936 [inline]
       do_splice+0xef8/0x1940 fs/splice.c:1349
       __do_splice fs/splice.c:1431 [inline]
       __do_sys_splice fs/splice.c:1634 [inline]
       __se_sys_splice+0x353/0x490 fs/splice.c:1616
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  cb_lock --> sb_writers#5 --> &pipe->mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex);
                               lock(sb_writers#5);
                               lock(&pipe->mutex);
  rlock(cb_lock);

 *** DEADLOCK ***

1 lock held by syz.5.3982/21304:
 #0: ffff88801129a858 (&pipe->mutex){+.+.}-{4:4}, at: splice_to_socket+0x15f/0x11f0 fs/splice.c:805

stack backtrace:
CPU: 0 UID: 0 PID: 21304 Comm: syz.5.3982 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2045
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2177
 check_prev_add kernel/locking/lockdep.c:3167 [inline]
 check_prevs_add kernel/locking/lockdep.c:3286 [inline]
 validate_chain kernel/locking/lockdep.c:3910 [inline]
 __lock_acquire+0x15a5/0x2d10 kernel/locking/lockdep.c:5239
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
 down_read+0x97/0x200 kernel/locking/rwsem.c:1568
 genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x780/0x920 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:797
 __sock_sendmsg net/socket.c:812 [inline]
 sock_sendmsg+0x1ca/0x2d0 net/socket.c:835
 splice_to_socket+0xae5/0x11f0 fs/splice.c:884
 do_splice_from fs/splice.c:936 [inline]
 do_splice+0xef8/0x1940 fs/splice.c:1349
 __do_splice fs/splice.c:1431 [inline]
 __do_sys_splice fs/splice.c:1634 [inline]
 __se_sys_splice+0x353/0x490 fs/splice.c:1616
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f64295dce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f64277ec028 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00007f6429856180 RCX: 00007f64295dce59
RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f6429672d6f R08: 000000000004ffe6 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6429856218 R14: 00007f6429856180 R15: 00007fffd9caba38
 </TASK>
loop5: detected capacity change from 0 to 512
EXT4-fs (loop5): mounted filesystem 00000000-0000-0000-0000-000000000000 r/w without journal. Quota mode: writeback.