====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ kworker/2:0/24 is trying to acquire lock: ffff88805ab8a2c8 (&tty->termios_rwsem){++++}-{4:4}, at: class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] ffff88805ab8a2c8 (&tty->termios_rwsem){++++}-{4:4}, at: n_tty_flush_buffer+0x25/0x1b0 drivers/tty/n_tty.c:349 but task is already holding lock: ffff88801c2c20b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:236 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #3 (&buf->lock){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821 tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:236 tty_ldisc_flush+0x68/0xf0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x368/0x480 drivers/tty/tty_io.c:3025 vc_SAK+0x7f/0x320 drivers/tty/vt/vt_ioctl.c:994 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322 process_scheduled_works kernel/workqueue.c:3405 [inline] worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486 kthread+0x370/0x450 kernel/kthread.c:436 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #2 (console_lock){+.+.}-{0:0}: lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825 console_lock+0x7a/0xa0 kernel/printk/printk.c:2896 uart_configure_port drivers/tty/serial/serial_core.c:2530 [inline] serial_core_add_one_port drivers/tty/serial/serial_core.c:3101 [inline] serial_core_register_port+0xe65/0x16f0 drivers/tty/serial/serial_core.c:3322 serial8250_register_8250_port+0x15af/0x2330 drivers/tty/serial/8250/8250_core.c:828 serial_pnp_probe+0x436/0x930 drivers/tty/serial/8250/8250_pnp.c:480 pnp_device_probe+0x2b3/0x4a0 drivers/pnp/driver.c:111 call_driver_probe drivers/base/dd.c:628 [inline] really_probe+0x241/0xa60 drivers/base/dd.c:706 __driver_probe_device+0x20e/0x450 drivers/base/dd.c:868 driver_probe_device+0x4a/0x140 drivers/base/dd.c:898 __driver_attach+0x21f/0x5b0 drivers/base/dd.c:1292 bus_for_each_dev+0x13e/0x1d0 drivers/base/bus.c:383 bus_add_driver+0x305/0x5b0 drivers/base/bus.c:763 driver_register+0x1e2/0x360 drivers/base/driver.c:174 serial8250_init+0xcc/0x1c0 drivers/tty/serial/8250/8250_platform.c:317 do_one_initcall+0x11d/0x700 init/main.c:1347 do_initcall_level init/main.c:1409 [inline] do_initcalls init/main.c:1425 [inline] do_basic_setup init/main.c:1445 [inline] kernel_init_freeable+0x6ea/0x7b0 init/main.c:1658 kernel_init+0x1f/0x1e0 init/main.c:1548 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 -> #1 (&port->mutex){+.+.}-{4:4}: lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825 __mutex_lock_common kernel/locking/mutex.c:646 [inline] __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821 class_mutex_constructor include/linux/mutex.h:253 [inline] uart_set_termios+0x8e/0x690 drivers/tty/serial/serial_core.c:1645 tty_set_termios+0x64d/0x980 drivers/tty/tty_ioctl.c:341 set_termios+0x5c8/0x880 drivers/tty/tty_ioctl.c:516 tty_mode_ioctl+0x17e/0xd40 drivers/tty/tty_ioctl.c:803 n_tty_ioctl_helper+0x47/0x2b0 drivers/tty/tty_ioctl.c:982 n_tty_ioctl+0x53/0x340 drivers/tty/n_tty.c:2496 tty_ioctl+0x11b4/0x1640 drivers/tty/tty_io.c:2801 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (&tty->termios_rwsem){++++}-{4:4}: check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165 check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237 lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825 down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631 class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] n_tty_flush_buffer+0x25/0x1b0 drivers/tty/n_tty.c:349 tty_buffer_flush+0x239/0x310 drivers/tty/tty_buffer.c:248 tty_ldisc_flush+0x68/0xf0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x368/0x480 drivers/tty/tty_io.c:3025 vc_SAK+0x7f/0x320 drivers/tty/vt/vt_ioctl.c:994 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322 process_scheduled_works kernel/workqueue.c:3405 [inline] worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486 kthread+0x370/0x450 kernel/kthread.c:436 ret_from_fork+0x72b/0xd50 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: &tty->termios_rwsem --> console_lock --> &buf->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&buf->lock); lock(console_lock); lock(&buf->lock); lock(&tty->termios_rwsem); *** DEADLOCK *** 5 locks held by kworker/2:0/24: #0: ffff88801bcaa940 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297 #1: ffffc9000062fd08 ((work_completion)(&vc_cons[currcons].SAK_work)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298 #2: ffffffff8ebd45a0 (console_lock){+.+.}-{0:0}, at: class_console_lock_constructor include/linux/console.h:734 [inline] #2: ffffffff8ebd45a0 (console_lock){+.+.}-{0:0}, at: vc_SAK+0x13/0x320 drivers/tty/vt/vt_ioctl.c:985 #3: ffff88805ab8a0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref drivers/tty/tty_ldisc.c:263 [inline] #3: ffff88805ab8a0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_flush+0x1c/0xf0 drivers/tty/tty_ldisc.c:386 #4: ffff88801c2c20b8 (&buf->lock){+.+.}-{4:4}, at: tty_buffer_flush+0x72/0x310 drivers/tty/tty_buffer.c:236 stack backtrace: CPU: 2 UID: 0 PID: 24 Comm: kworker/2:0 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: events vc_SAK Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120 print_circular_bug.cold+0x178/0x1c7 kernel/locking/lockdep.c:2043 check_noncircular+0x146/0x160 kernel/locking/lockdep.c:2175 check_prev_add+0xeb/0xe60 kernel/locking/lockdep.c:3165 check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x136c/0x1a40 kernel/locking/lockdep.c:5237 lock_acquire kernel/locking/lockdep.c:5868 [inline] lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825 down_write+0x8b/0x1f0 kernel/locking/rwsem.c:1631 class_rwsem_write_constructor include/linux/rwsem.h:270 [inline] n_tty_flush_buffer+0x25/0x1b0 drivers/tty/n_tty.c:349 tty_buffer_flush+0x239/0x310 drivers/tty/tty_buffer.c:248 tty_ldisc_flush+0x68/0xf0 drivers/tty/tty_ldisc.c:388 __do_SAK+0x368/0x480 drivers/tty/tty_io.c:3025 vc_SAK+0x7f/0x320 drivers/tty/vt/vt_ioctl.c:994 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322 process_scheduled_works kernel/workqueue.c:3405 [inline] worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486 kthread+0x370/0x450 kernel/kthread.c:436 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245