====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:0/9 is trying to acquire lock: ffff88801b07a0b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:236 but task is already holding lock: ffffffff8eb4bfa0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] ffffffff8eb4bfa0 (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:2896 class_console_lock_constructor include/linux/console.h:734 [inline] con_flush_chars+0x6c/0x80 drivers/tty/vt/vt.c:3730 __receive_buf drivers/tty/n_tty.c:1620 [inline] n_tty_receive_buf_common+0xd2a/0x13d0 drivers/tty/n_tty.c:1715 tty_port_default_receive_buf+0x6e/0xa0 drivers/tty/tty_port.c:37 receive_buf drivers/tty/tty_buffer.c:452 [inline] flush_to_ldisc+0x247/0x6c0 drivers/tty/tty_buffer.c:502 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 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 -> #1 (&tty->termios_rwsem){++++}-{4:4}: down_read+0x4a/0x330 kernel/locking/rwsem.c:1574 class_rwsem_read_constructor include/linux/rwsem.h:259 [inline] n_tty_receive_buf_common+0x84/0x13d0 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:452 [inline] flush_to_ldisc+0x247/0x6c0 drivers/tty/tty_buffer.c:502 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 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 -> #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+0x1520/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x25e/0x680 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 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 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/0:0/9: #0: ffff88801b02b140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #0: ffff88801b02b140 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405 #1: ffffc900000e7c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #1: ffffc900000e7c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0xa20/0x14e0 kernel/workqueue.c:3405 #2: ffffffff8eb4bfa0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] #2: ffffffff8eb4bfa0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985 #3: ffff88805433e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline] #3: ffff88805433e0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386 stack backtrace: CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026 Workqueue: events vc_SAK Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e1/0x300 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+0x1520/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x19d/0x1550 kernel/locking/mutex.c:821 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x25e/0x680 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 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