======================================================
WARNING: possible circular locking dependency detected
5.12.0-rc6-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.4/27949 is trying to acquire lock:
ffffffff8c704c60 (console_owner){-...}-{0:0}, at: console_trylock_spinning+0x10e/0x2f0 kernel/printk/printk.c:1788

but task is already holding lock:
ffff88801aaf9158 (&port->lock){-.-.}-{2:2}, at: pty_write+0xb6/0x170 drivers/tty/pty.c:119

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&port->lock){-.-.}-{2:2}:
       lock_acquire+0x126/0x650 kernel/locking/lockdep.c:5510
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x73/0xa0 kernel/locking/spinlock.c:159
       tty_port_tty_get+0x21/0xe0 drivers/tty/tty_port.c:288
       tty_port_default_wakeup+0x11/0x40 drivers/tty/tty_port.c:47
       serial8250_tx_chars+0x5ea/0x800 drivers/tty/serial/8250/8250_port.c:1832
       serial8250_handle_irq+0x2fd/0x3e0 drivers/tty/serial/8250/8250_port.c:1919
       serial8250_default_handle_irq+0xaf/0x190 drivers/tty/serial/8250/8250_port.c:1935
       serial8250_interrupt+0xa3/0x1e0 drivers/tty/serial/8250/8250_core.c:126
       __handle_irq_event_percpu+0x1b7/0x620 kernel/irq/handle.c:156
       handle_irq_event_percpu kernel/irq/handle.c:196 [inline]
       handle_irq_event+0xbd/0x280 kernel/irq/handle.c:213
       handle_edge_irq+0x245/0xbe0 kernel/irq/chip.c:819
       generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
       handle_irq arch/x86/kernel/irq.c:231 [inline]
       __common_interrupt+0xce/0x1e0 arch/x86/kernel/irq.c:250
       common_interrupt+0x9c/0xc0 arch/x86/kernel/irq.c:240
       asm_common_interrupt+0x1e/0x40 arch/x86/include/asm/idtentry.h:623
       __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
       _raw_spin_unlock_irqrestore+0x7a/0xc0 kernel/locking/spinlock.c:191
       spin_unlock_irqrestore include/linux/spinlock.h:409 [inline]
       uart_write+0x6a1/0x8f0 drivers/tty/serial/serial_core.c:615
       do_output_char+0x638/0x940 drivers/tty/n_tty.c:443
       process_output drivers/tty/n_tty.c:510 [inline]
       n_tty_write+0xd5c/0x1180 drivers/tty/n_tty.c:2365
       do_tty_write drivers/tty/tty_io.c:1043 [inline]
       file_tty_write+0x5c5/0x9a0 drivers/tty/tty_io.c:1133
       do_iter_readv_writev+0x48c/0x650 include/linux/fs.h:1971
       do_iter_write+0x16c/0x5f0 fs/read_write.c:866
       vfs_writev fs/read_write.c:939 [inline]
       do_writev+0x19a/0x350 fs/read_write.c:982
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #1 (&port_lock_key){-.-.}-{2:2}:
       lock_acquire+0x126/0x650 kernel/locking/lockdep.c:5510
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x73/0xa0 kernel/locking/spinlock.c:159
       serial8250_console_write+0x107/0xd20 drivers/tty/serial/8250/8250_port.c:3292
       call_console_drivers kernel/printk/printk.c:1858 [inline]
       console_unlock+0x930/0xe00 kernel/printk/printk.c:2576
       vprintk_emit+0x1ab/0x270 kernel/printk/printk.c:2098
       printk+0x62/0x83 kernel/printk/printk.c:2146
       register_console+0x802/0xad0 kernel/printk/printk.c:2927
       univ8250_console_init+0x41/0x43 drivers/tty/serial/8250/8250_core.c:690
       console_init+0x52/0x97 kernel/printk/printk.c:3027
       start_kernel+0x30c/0x544 init/main.c:993
       secondary_startup_64_no_verify+0xb0/0xbb

-> #0 (console_owner){-...}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:2936 [inline]
       check_prevs_add+0x339/0x5c20 kernel/locking/lockdep.c:3059
       validate_chain kernel/locking/lockdep.c:3674 [inline]
       __lock_acquire+0x41f7/0x5e60 kernel/locking/lockdep.c:4900
       lock_acquire+0x126/0x650 kernel/locking/lockdep.c:5510
       console_trylock_spinning+0x12e/0x2f0 kernel/printk/printk.c:1805
       vprintk_emit+0x192/0x270 kernel/printk/printk.c:2097
       printk+0x62/0x83 kernel/printk/printk.c:2146
       fail_dump lib/fault-inject.c:45 [inline]
       should_fail+0x366/0x4b0 lib/fault-inject.c:146
       should_failslab+0x5/0x20 mm/slab_common.c:1273
       slab_pre_alloc_hook mm/slab.h:499 [inline]
       slab_alloc_node mm/slub.c:2826 [inline]
       slab_alloc mm/slub.c:2915 [inline]
       __kmalloc+0x89/0x380 mm/slub.c:4051
       kmalloc include/linux/slab.h:559 [inline]
       tty_buffer_alloc drivers/tty/tty_buffer.c:175 [inline]
       __tty_buffer_request_room+0x1f0/0x540 drivers/tty/tty_buffer.c:273
       tty_insert_flip_string_fixed_flag+0x92/0x2c0 drivers/tty/tty_buffer.c:318
       tty_insert_flip_string include/linux/tty_flip.h:37 [inline]
       pty_write+0xda/0x170 drivers/tty/pty.c:121
       tty_put_char+0xc7/0x110 drivers/tty/tty_io.c:3182
       __process_echoes+0x1a9/0x930 drivers/tty/n_tty.c:742
       flush_echoes drivers/tty/n_tty.c:825 [inline]
       __receive_buf drivers/tty/n_tty.c:1644 [inline]
       n_tty_receive_buf_common+0x2a1a/0x3120 drivers/tty/n_tty.c:1739
       tiocsti drivers/tty/tty_io.c:2316 [inline]
       tty_ioctl+0xc64/0x15f0 drivers/tty/tty_io.c:2717
       vfs_ioctl fs/ioctl.c:48 [inline]
       __do_sys_ioctl fs/ioctl.c:753 [inline]
       __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:739
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

Chain exists of:
  console_owner --> &port_lock_key --> &port->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&port->lock);
                               lock(&port_lock_key);
                               lock(&port->lock);
  lock(console_owner);

 *** DEADLOCK ***

4 locks held by syz-executor.4/27949:
 #0: ffff888079ad0098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x21/0x70 drivers/tty/tty_ldisc.c:266
 #1: ffff888079ad02e8 (&o_tty->termios_rwsem/1){++++}-{3:3}, at: n_tty_receive_buf_common+0x88/0x3120 drivers/tty/n_tty.c:1702
 #2: ffffc90001538378 (&ldata->output_lock){+.+.}-{3:3}, at: flush_echoes drivers/tty/n_tty.c:823 [inline]
 #2: ffffc90001538378 (&ldata->output_lock){+.+.}-{3:3}, at: __receive_buf drivers/tty/n_tty.c:1644 [inline]
 #2: ffffc90001538378 (&ldata->output_lock){+.+.}-{3:3}, at: n_tty_receive_buf_common+0x29db/0x3120 drivers/tty/n_tty.c:1739
 #3: ffff88801aaf9158 (&port->lock){-.-.}-{2:2}, at: pty_write+0xb6/0x170 drivers/tty/pty.c:119

stack backtrace:
CPU: 1 PID: 27949 Comm: syz-executor.4 Not tainted 5.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x176/0x24e lib/dump_stack.c:120
 print_circular_bug+0xadf/0xd80 kernel/locking/lockdep.c:2005
 check_noncircular+0x221/0x2d0 kernel/locking/lockdep.c:2127
 check_prev_add kernel/locking/lockdep.c:2936 [inline]
 check_prevs_add+0x339/0x5c20 kernel/locking/lockdep.c:3059
 validate_chain kernel/locking/lockdep.c:3674 [inline]
 __lock_acquire+0x41f7/0x5e60 kernel/locking/lockdep.c:4900
 lock_acquire+0x126/0x650 kernel/locking/lockdep.c:5510
 console_trylock_spinning+0x12e/0x2f0 kernel/printk/printk.c:1805
 vprintk_emit+0x192/0x270 kernel/printk/printk.c:2097
 printk+0x62/0x83 kernel/printk/printk.c:2146
 fail_dump lib/fault-inject.c:45 [inline]
 should_fail+0x366/0x4b0 lib/fault-inject.c:146
 should_failslab+0x5/0x20 mm/slab_common.c:1273
 slab_pre_alloc_hook mm/slab.h:499 [inline]
 slab_alloc_node mm/slub.c:2826 [inline]
 slab_alloc mm/slub.c:2915 [inline]
 __kmalloc+0x89/0x380 mm/slub.c:4051
 kmalloc include/linux/slab.h:559 [inline]
 tty_buffer_alloc drivers/tty/tty_buffer.c:175 [inline]
 __tty_buffer_request_room+0x1f0/0x540 drivers/tty/tty_buffer.c:273
 tty_insert_flip_string_fixed_flag+0x92/0x2c0 drivers/tty/tty_buffer.c:318
 tty_insert_flip_string include/linux/tty_flip.h:37 [inline]
 pty_write+0xda/0x170 drivers/tty/pty.c:121
 tty_put_char+0xc7/0x110 drivers/tty/tty_io.c:3182
 __process_echoes+0x1a9/0x930 drivers/tty/n_tty.c:742
 flush_echoes drivers/tty/n_tty.c:825 [inline]
 __receive_buf drivers/tty/n_tty.c:1644 [inline]
 n_tty_receive_buf_common+0x2a1a/0x3120 drivers/tty/n_tty.c:1739
 tiocsti drivers/tty/tty_io.c:2316 [inline]
 tty_ioctl+0xc64/0x15f0 drivers/tty/tty_io.c:2717
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:739
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x466459
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fac16330188 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000056bf60 RCX: 0000000000466459
RDX: 0000000020000100 RSI: 0000000000005412 RDI: 0000000000000004
RBP: 00007fac163301d0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffdf649c16f R14: 00007fac16330300 R15: 0000000000022000