====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Tainted: G L ------------------------------------------------------ kworker/0:4/5876 is trying to acquire lock: ffff88813fe6a0b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 but task is already holding lock: ffffffff8eb517c0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:736 [inline] ffffffff8eb517c0 (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:736 [inline] con_flush_chars+0x6c/0x80 drivers/tty/vt/vt.c:3627 n_tty_write+0xf7e/0x12a0 drivers/tty/n_tty.c:2382 iterate_tty_write drivers/tty/tty_io.c:1006 [inline] file_tty_write+0x559/0xa20 drivers/tty/tty_io.c:1081 new_sync_write fs/read_write.c:595 [inline] vfs_write+0x61d/0xb90 fs/read_write.c:688 ksys_write+0x150/0x270 fs/read_write.c:740 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #1 (&tty->termios_rwsem){++++}-{4:4}: down_write+0x96/0x200 kernel/locking/rwsem.c:1590 class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] n_tty_flush_buffer+0x30/0x290 drivers/tty/n_tty.c:349 tty_buffer_flush+0x1ec/0x2b0 drivers/tty/tty_buffer.c:241 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 tty_port_close_start+0x388/0x580 drivers/tty/tty_port.c:627 tty_port_close+0x2a/0x170 drivers/tty/tty_port.c:682 tty_release+0x389/0x1710 drivers/tty/tty_io.c:1745 __fput+0x44f/0xa70 fs/file_table.c:469 task_work_run+0x1d9/0x270 kernel/task_work.c:233 exit_task_work include/linux/task_work.h:40 [inline] do_exit+0x926/0x2490 kernel/exit.c:974 do_group_exit+0x21b/0x2d0 kernel/exit.c:1116 get_signal+0x1284/0x1330 kernel/signal.c:3035 arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline] exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:269 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline] do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:614 [inline] __mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0xf2/0x6e0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work+0x9ab/0x1780 kernel/workqueue.c:3289 process_scheduled_works kernel/workqueue.c:3380 [inline] worker_thread+0xb49/0x1140 kernel/workqueue.c:3461 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x51e/0xb90 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/0:4/5876: #0: ffff88813fe03148 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x894/0x1780 kernel/workqueue.c:3261 #1: ffffc90004647c40 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x8bb/0x1780 kernel/workqueue.c:3262 #2: ffffffff8eb517c0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:736 [inline] #2: ffffffff8eb517c0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:985 #3: ffff8880261c80a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline] #3: ffff8880261c80a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x20/0xc0 drivers/tty/tty_ldisc.c:386 stack backtrace: CPU: 0 UID: 0 PID: 5876 Comm: kworker/0:4 Tainted: G L syzkaller #0 PREEMPT(full) Tainted: [L]=SOFTLOCKUP Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/27/2026 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+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0xf0/0x2e0 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:614 [inline] __mutex_lock+0x19f/0x1300 kernel/locking/mutex.c:776 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 tty_ldisc_flush+0x6b/0xc0 drivers/tty/tty_ldisc.c:388 __do_SAK+0xf2/0x6e0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:994 process_one_work+0x9ab/0x1780 kernel/workqueue.c:3289 process_scheduled_works kernel/workqueue.c:3380 [inline] worker_thread+0xb49/0x1140 kernel/workqueue.c:3461 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 tty tty1: SAK: killed process 24724 (syz.3.6739): by fd#9 tty tty1: SAK: killed process 24725 (syz.3.6739): by fd#9 tty tty1: SAK: killed process 24729 (syz.3.6739): by fd#9