====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ udevd/9103 is trying to acquire lock: ffff888077cd1938 ((wq_completion)loop1){+.+.}-{0:0}, at: flush_workqueue+0x150/0x13d0 kernel/workqueue.c:2830 but task is already holding lock: ffff888147691468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xaa/0xb90 drivers/block/loop.c:1366 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #7 (&lo->lo_mutex){+.+.}-{3:3}: __mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596 __mutex_lock kernel/locking/mutex.c:729 [inline] mutex_lock_killable_nested+0x17/0x20 kernel/locking/mutex.c:758 lo_open+0x6a/0x100 drivers/block/loop.c:2056 blkdev_get_whole+0x90/0x390 block/bdev.c:669 blkdev_get_by_dev+0x2d0/0xa60 block/bdev.c:827 blkdev_open+0x12d/0x2c0 block/fops.c:466 do_dentry_open+0x7ff/0xf80 fs/open.c:826 do_open fs/namei.c:3616 [inline] path_openat+0x26f5/0x2fa0 fs/namei.c:3750 do_filp_open+0x1e2/0x410 fs/namei.c:3777 do_sys_openat2+0x150/0x4b0 fs/open.c:1255 do_sys_open fs/open.c:1271 [inline] __do_sys_openat fs/open.c:1287 [inline] __se_sys_openat fs/open.c:1282 [inline] __x64_sys_openat+0x135/0x160 fs/open.c:1282 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 -> #6 (&disk->open_mutex){+.+.}-{3:3}: __mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596 __mutex_lock kernel/locking/mutex.c:729 [inline] mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743 bd_register_pending_holders+0x33/0x310 block/holder.c:161 device_add_disk+0x5a7/0xd40 block/genhd.c:486 add_disk include/linux/genhd.h:200 [inline] nbd_dev_add+0x757/0xb20 drivers/block/nbd.c:1786 nbd_genl_connect+0x850/0x18a0 drivers/block/nbd.c:1927 genl_family_rcv_msg_doit net/netlink/genetlink.c:731 [inline] genl_family_rcv_msg net/netlink/genetlink.c:775 [inline] genl_rcv_msg+0xcea/0xf90 net/netlink/genetlink.c:792 netlink_rcv_skb+0x1f5/0x440 net/netlink/af_netlink.c:2507 genl_rcv+0x24/0x40 net/netlink/genetlink.c:803 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x774/0x920 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918 sock_sendmsg_nosec net/socket.c:706 [inline] __sock_sendmsg net/socket.c:718 [inline] ____sys_sendmsg+0x5b7/0x8f0 net/socket.c:2445 ___sys_sendmsg+0x236/0x2e0 net/socket.c:2499 __sys_sendmsg net/socket.c:2528 [inline] __do_sys_sendmsg net/socket.c:2537 [inline] __se_sys_sendmsg+0x1af/0x290 net/socket.c:2535 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 -> #5 (genl_mutex){+.+.}-{3:3}: __mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596 __mutex_lock kernel/locking/mutex.c:729 [inline] mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743 genl_lock net/netlink/genetlink.c:33 [inline] genl_lock_all net/netlink/genetlink.c:46 [inline] genl_register_family+0x3f0/0x10f0 net/netlink/genetlink.c:393 vdpa_init+0x35/0x70 drivers/vdpa/vdpa.c:903 do_one_initcall+0x272/0x730 init/main.c:1316 do_initcall_level+0x137/0x1f0 init/main.c:1389 do_initcalls+0x4b/0x90 init/main.c:1405 kernel_init_freeable+0x3e9/0x570 init/main.c:1629 kernel_init+0x19/0x1b0 init/main.c:1520 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287 -> #4 (cb_lock){++++}-{3:3}: down_read+0x44/0x2e0 kernel/locking/rwsem.c:1498 genl_rcv+0x15/0x40 net/netlink/genetlink.c:802 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x774/0x920 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1918 sock_sendmsg_nosec net/socket.c:706 [inline] __sock_sendmsg net/socket.c:718 [inline] sock_sendmsg net/socket.c:741 [inline] kernel_sendmsg+0x234/0x350 net/socket.c:765 sock_no_sendpage+0x12a/0x1a0 net/core/sock.c:3045 kernel_sendpage+0x2cb/0x380 net/socket.c:3548 sock_sendpage+0x7a/0xb0 net/socket.c:1027 pipe_to_sendpage+0x22f/0x320 fs/splice.c:364 splice_from_pipe_feed fs/splice.c:418 [inline] __splice_from_pipe+0x302/0x820 fs/splice.c:562 splice_from_pipe fs/splice.c:597 [inline] generic_splice_sendpage+0x111/0x180 fs/splice.c:746 do_splice_from fs/splice.c:767 [inline] do_splice+0xe5a/0x1640 fs/splice.c:1108 __do_splice fs/splice.c:1173 [inline] __do_sys_splice fs/splice.c:1379 [inline] __se_sys_splice+0x34d/0x440 fs/splice.c:1361 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 -> #3 (&pipe->mutex/1){+.+.}-{3:3}: __mutex_lock_common+0x1e3/0x2400 kernel/locking/mutex.c:596 __mutex_lock kernel/locking/mutex.c:729 [inline] mutex_lock_nested+0x17/0x20 kernel/locking/mutex.c:743 iter_file_splice_write+0x1b5/0xcc0 fs/splice.c:635 do_splice_from fs/splice.c:767 [inline] do_splice+0xe5a/0x1640 fs/splice.c:1108 __do_splice fs/splice.c:1173 [inline] __do_sys_splice fs/splice.c:1379 [inline] __se_sys_splice+0x34d/0x440 fs/splice.c:1361 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x66/0xd0 -> #2 (sb_writers#3){.+.+}-{0:0}: percpu_down_read include/linux/percpu-rwsem.h:51 [inline] __sb_start_write include/linux/fs.h:1811 [inline] sb_start_write include/linux/fs.h:1881 [inline] file_start_write include/linux/fs.h:3043 [inline] lo_write_bvec+0x1a0/0x780 drivers/block/loop.c:315 lo_write_simple drivers/block/loop.c:338 [inline] do_req_filebacked drivers/block/loop.c:656 [inline] loop_handle_cmd drivers/block/loop.c:2235 [inline] loop_process_work+0x1b46/0x24a0 drivers/block/loop.c:2275 process_one_work+0x85f/0x1010 kernel/workqueue.c:2310 worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457 kthread+0x436/0x520 kernel/kthread.c:334 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287 -> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}: process_one_work+0x7bb/0x1010 kernel/workqueue.c:2286 worker_thread+0xaa6/0x1290 kernel/workqueue.c:2457 kthread+0x436/0x520 kernel/kthread.c:334 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287 -> #0 ((wq_completion)loop1){+.+.}-{0:0}: check_prev_add kernel/locking/lockdep.c:3053 [inline] check_prevs_add kernel/locking/lockdep.c:3172 [inline] validate_chain kernel/locking/lockdep.c:3788 [inline] __lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623 flush_workqueue+0x16c/0x13d0 kernel/workqueue.c:2830 drain_workqueue+0xcf/0x380 kernel/workqueue.c:2995 destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439 __loop_clr_fd+0x234/0xb90 drivers/block/loop.c:1384 blkdev_put_whole block/bdev.c:692 [inline] blkdev_put+0x53f/0x7d0 block/bdev.c:957 blkdev_close+0x76/0xa0 block/fops.c:478 __fput+0x234/0x930 fs/file_table.c:311 task_work_run+0x125/0x1a0 kernel/task_work.c:188 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline] syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x66/0xd0 other info that might help us debug this: Chain exists of: (wq_completion)loop1 --> &disk->open_mutex --> &lo->lo_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lo->lo_mutex); lock(&disk->open_mutex); lock(&lo->lo_mutex); lock((wq_completion)loop1); *** DEADLOCK *** 2 locks held by udevd/9103: #0: ffff88802045e518 (&disk->open_mutex){+.+.}-{3:3}, at: blkdev_put+0xf9/0x7d0 block/bdev.c:915 #1: ffff888147691468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0xaa/0xb90 drivers/block/loop.c:1366 stack backtrace: CPU: 1 PID: 9103 Comm: udevd Not tainted syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 Call Trace: dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133 check_prev_add kernel/locking/lockdep.c:3053 [inline] check_prevs_add kernel/locking/lockdep.c:3172 [inline] validate_chain kernel/locking/lockdep.c:3788 [inline] __lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623 flush_workqueue+0x16c/0x13d0 kernel/workqueue.c:2830 drain_workqueue+0xcf/0x380 kernel/workqueue.c:2995 destroy_workqueue+0x7b/0xb20 kernel/workqueue.c:4439 __loop_clr_fd+0x234/0xb90 drivers/block/loop.c:1384 blkdev_put_whole block/bdev.c:692 [inline] blkdev_put+0x53f/0x7d0 block/bdev.c:957 blkdev_close+0x76/0xa0 block/fops.c:478 __fput+0x234/0x930 fs/file_table.c:311 task_work_run+0x125/0x1a0 kernel/task_work.c:188 tracehook_notify_resume include/linux/tracehook.h:189 [inline] exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline] syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86 entry_SYSCALL_64_after_hwframe+0x66/0xd0 RIP: 0033:0x7f8fcc667407 Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff RSP: 002b:00007ffe5bb77e60 EFLAGS: 00000202 ORIG_RAX: 0000000000000003 RAX: 0000000000000000 RBX: 00007f8fcc579880 RCX: 00007f8fcc667407 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000008 RBP: 00007f8fcc5796e8 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000002 R13: 00005630ee5fb410 R14: 0000000000000008 R15: 00005630ee5fbe00