====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/0:2/54 is trying to acquire lock: ffff88801a4c90b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 but task is already holding lock: ffffffff8e12e380 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:999 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (console_lock){+.+.}-{0:0}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 console_lock+0x164/0x1b0 kernel/printk/printk.c:2849 con_flush_chars+0x70/0x280 drivers/tty/vt/vt.c:3585 __receive_buf drivers/tty/n_tty.c:1628 [inline] n_tty_receive_buf_common+0xc8b/0x12f0 drivers/tty/n_tty.c:1723 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:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #1 (&tty->termios_rwsem){++++}-{4:4}: lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 down_read+0x46/0x2e0 kernel/locking/rwsem.c:1537 n_tty_receive_buf_common+0x84/0x12f0 drivers/tty/n_tty.c:1686 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:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 __do_SAK+0xf2/0x6e0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:1009 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148 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 *** 3 locks held by kworker/0:2/54: #0: ffff88801a474d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline] #0: ffff88801a474d48 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0 kernel/workqueue.c:3319 #1: ffffc9000101fbc0 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline] #1: ffffc9000101fbc0 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0 kernel/workqueue.c:3319 #2: ffffffff8e12e380 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x28/0x220 drivers/tty/vt/vt_ioctl.c:999 stack backtrace: CPU: 0 UID: 0 PID: 54 Comm: kworker/0:2 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: events vc_SAK Call Trace: dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043 check_noncircular+0x134/0x160 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+0xb9b/0x2140 kernel/locking/lockdep.c:3908 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868 __mutex_lock_common kernel/locking/mutex.c:598 [inline] __mutex_lock+0x187/0x1350 kernel/locking/mutex.c:760 tty_buffer_flush+0x74/0x2b0 drivers/tty/tty_buffer.c:229 __do_SAK+0xf2/0x6e0 drivers/tty/tty_io.c:3025 vc_SAK+0x78/0x220 drivers/tty/vt/vt_ioctl.c:1009 process_one_work kernel/workqueue.c:3236 [inline] process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400 kthread+0x70e/0x8a0 kernel/kthread.c:463 ret_from_fork+0x436/0x7d0 arch/x86/kernel/process.c:148 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 usb 5-1: USB disconnect, device number 27 usb 5-1: new high-speed USB device number 28 using dummy_hcd usb 5-1: config 0 interface 0 altsetting 0 endpoint 0x81 has an invalid bInterval 0, changing to 7 usb 5-1: New USB device found, idVendor=0926, idProduct=3333, bcdDevice= 0.40 usb 5-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0 usb 5-1: config 0 descriptor?? keytouch 0003:0926:3333.009A: fixing up Keytouch IEC report descriptor input: HID 0926:3333 as /devices/platform/dummy_hcd.0/usb5/5-1/5-1:0.0/0003:0926:3333.009A/input/input157 keytouch 0003:0926:3333.009A: input,hidraw1: USB HID v0.00 Keyboard [HID 0926:3333] on usb-dummy_hcd.0-1/input0 usb 5-1: USB disconnect, device number 28 usb 5-1: USB disconnect, device number 30 usb 5-1: new high-speed USB device number 31 using dummy_hcd usb 5-1: config 0 interface 0 altsetting 0 endpoint 0x81 has an invalid bInterval 0, changing to 7 usb 5-1: New USB device found, idVendor=0926, idProduct=3333, bcdDevice= 0.40 usb 5-1: New USB device strings: Mfr=0, Product=0, SerialNumber=0 usb 5-1: config 0 descriptor?? keytouch 0003:0926:3333.009D: fixing up Keytouch IEC report descriptor input: HID 0926:3333 as /devices/platform/dummy_hcd.0/usb5/5-1/5-1:0.0/0003:0926:3333.009D/input/input160 keytouch 0003:0926:3333.009D: input,hidraw1: USB HID v0.00 Keyboard [HID 0926:3333] on usb-dummy_hcd.0-1/input0