====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ kworker/1:16/16640 is trying to acquire lock: ffff88813ff730a8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 but task is already holding lock: ffffffff8d5a25e0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:737 [inline] ffffffff8d5a25e0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (console_lock){+.+.}-{0:0}: console_lock+0x76/0x90 kernel/printk/printk.c:2843 class_console_lock_constructor include/linux/console.h:737 [inline] con_flush_chars+0x9d/0x2c0 drivers/tty/vt/vt.c:3634 n_tty_write+0xf78/0x12a0 drivers/tty/n_tty.c:2382 iterate_tty_write drivers/tty/tty_io.c:1006 [inline] file_tty_write+0x562/0xa30 drivers/tty/tty_io.c:1081 new_sync_write fs/read_write.c:593 [inline] vfs_write+0x5d5/0xb40 fs/read_write.c:686 ksys_write+0x14b/0x260 fs/read_write.c:738 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&tty->termios_rwsem){++++}-{4:4}: down_read+0x97/0x1f0 kernel/locking/rwsem.c:1537 class_rwsem_read_constructor include/linux/rwsem.h:253 [inline] n_tty_receive_buf_common+0x84/0x1300 drivers/tty/n_tty.c:1678 tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37 receive_buf drivers/tty/tty_buffer.c:445 [inline] flush_to_ldisc+0x24a/0x6e0 drivers/tty/tty_buffer.c:495 process_one_work kernel/workqueue.c:3257 [inline] process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 -> #0 (&buf->lock){+.+.}-{4:4}: 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline] mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0xe3/0x6d0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3257 [inline] process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 other info that might help us debug this: Chain exists of: &buf->lock --> &tty->termios_rwsem --> console_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(console_lock); lock(&tty->termios_rwsem); lock(console_lock); lock(&buf->lock); *** DEADLOCK *** 4 locks held by kworker/1:16/16640: #0: ffff88813ff55138 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3232 [inline] #0: ffff88813ff55138 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x1770 kernel/workqueue.c:3340 #1: ffffc90005a47b80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3233 [inline] #1: ffffc90005a47b80 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x1770 kernel/workqueue.c:3340 #2: ffffffff8d5a25e0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:737 [inline] #2: ffffffff8d5a25e0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985 #3: ffff888032c290a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline] #3: ffff888032c290a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386 stack backtrace: CPU: 1 UID: 0 PID: 16640 Comm: kworker/1:16 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)} Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 Workqueue: events vc_SAK Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2043 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2175 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+0x15a6/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x117/0x340 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/rtmutex_api.c:533 [inline] mutex_lock_nested+0x5a/0x1d0 kernel/locking/rtmutex_api.c:552 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0xe3/0x6d0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3257 [inline] process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421 kthread+0x711/0x8a0 kernel/kthread.c:463 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246 tty tty1: SAK: killed process 9302 (syz.0.1020): by fd#3 usb 9-1: new high-speed USB device number 7 using dummy_hcd usb 9-1: device descriptor read/64, error -71 usb 9-1: new high-speed USB device number 8 using dummy_hcd usb 9-1: device descriptor read/64, error -71 usb usb9-port1: attempt power cycle usb 9-1: new high-speed USB device number 9 using dummy_hcd usb 9-1: device descriptor read/8, error -71 usb 9-1: new high-speed USB device number 10 using dummy_hcd usb 9-1: device descriptor read/8, error -71 usb usb9-port1: unable to enumerate USB device