====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/1:2/867 is trying to acquire lock: ffff0000d86d10b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 but task is already holding lock: ffff800088cec860 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] ffff800088cec860 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x2c/0xa4 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+0x8c/0xac kernel/printk/printk.c:2896 class_console_lock_constructor include/linux/console.h:734 [inline] con_flush_chars+0x7c/0xc0 drivers/tty/vt/vt.c:3730 __receive_buf drivers/tty/n_tty.c:1620 [inline] n_tty_receive_buf_common+0xa6c/0xff4 drivers/tty/n_tty.c:1715 n_tty_receive_buf+0x40/0x54 drivers/tty/n_tty.c:1753 tiocsti+0x234/0x2ec drivers/tty/tty_io.c:2290 tty_ioctl+0x38c/0xd50 drivers/tty/tty_io.c:2706 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __arm64_sys_ioctl+0x154/0x1cc fs/ioctl.c:583 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594 -> #1 (&tty->termios_rwsem){++++}-{4:4}: down_read+0x58/0x2bc kernel/locking/rwsem.c:1574 class_rwsem_read_constructor include/linux/rwsem.h:259 [inline] n_tty_receive_buf_common+0x70/0xff4 drivers/tty/n_tty.c:1678 n_tty_receive_buf+0x40/0x54 drivers/tty/n_tty.c:1753 tiocsti+0x234/0x2ec drivers/tty/tty_io.c:2290 tty_ioctl+0x38c/0xd50 drivers/tty/tty_io.c:2706 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __arm64_sys_ioctl+0x154/0x1cc fs/ioctl.c:583 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:736 el0t_64_sync_handler+0x48/0x148 arch/arm64/kernel/entry-common.c:755 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:594 -> #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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237 lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x30/0x7c drivers/tty/tty_ldisc.c:388 __do_SAK+0x21c/0x604 drivers/tty/tty_io.c:3025 vc_SAK+0x74/0xa4 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486 kthread+0x304/0x3d4 kernel/kthread.c:436 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842 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/1:2/867: #0: ffff0000c002b540 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #0: ffff0000c002b540 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x734/0x10b8 kernel/workqueue.c:3405 #1: ffff800094887c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3297 [inline] #1: ffff800094887c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x73c/0x10b8 kernel/workqueue.c:3405 #2: ffff800088cec860 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] #2: ffff800088cec860 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x2c/0xa4 drivers/tty/vt/vt_ioctl.c:985 #3: ffff0000c62bd0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x20/0x90 drivers/tty/tty_ldisc.c:263 stack backtrace: CPU: 1 UID: 0 PID: 867 Comm: kworker/1:2 Not tainted syzkaller #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/02/2026 Workqueue: events vc_SAK Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_circular_bug+0x328/0x330 kernel/locking/lockdep.c:2043 check_noncircular+0x158/0x174 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+0x17c0/0x2ebc kernel/locking/lockdep.c:5237 lock_acquire+0x140/0x364 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x164/0xf14 kernel/locking/mutex.c:821 mutex_lock_nested+0x24/0x30 kernel/locking/mutex.c:874 tty_buffer_flush+0x78/0x2b4 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x30/0x7c drivers/tty/tty_ldisc.c:388 __do_SAK+0x21c/0x604 drivers/tty/tty_io.c:3025 vc_SAK+0x74/0xa4 drivers/tty/vt/vt_ioctl.c:994 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0x788/0x10b8 kernel/workqueue.c:3405 worker_thread+0x798/0xbd0 kernel/workqueue.c:3486 kthread+0x304/0x3d4 kernel/kthread.c:436 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:842