FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.568/6665 is trying to acquire lock:
ffffffff8c313580 (console_owner){-.-.}-{0:0}, at: console_lock_spinning_enable+0x2c/0x60 kernel/printk/printk.c:1802

but task is already holding lock:
ffff88802392a158 (&port->lock){-...}-{2:2}, at: tty_insert_flip_string_and_push_buffer+0x39/0x370 drivers/tty/tty_buffer.c:585

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&port->lock){-...}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xb0/0x100 kernel/locking/spinlock.c:162
       tty_port_tty_get drivers/tty/tty_port.c:289 [inline]
       tty_port_default_wakeup+0x1f/0xf0 drivers/tty/tty_port.c:48
       serial8250_tx_chars+0x629/0x830 drivers/tty/serial/8250/8250_port.c:1828
       serial8250_handle_irq+0x519/0x610 drivers/tty/serial/8250/8250_port.c:1924
       serial8250_default_handle_irq+0xb4/0x1a0 drivers/tty/serial/8250/8250_port.c:1941
       serial8250_interrupt+0x9b/0x1c0 drivers/tty/serial/8250/8250_core.c:127
       __handle_irq_event_percpu+0x299/0x9d0 kernel/irq/handle.c:156
       handle_irq_event_percpu kernel/irq/handle.c:196 [inline]
       handle_irq_event+0xa5/0x220 kernel/irq/handle.c:213
       handle_edge_irq+0x243/0xb20 kernel/irq/chip.c:819
       generic_handle_irq_desc include/linux/irqdesc.h:158 [inline]
       handle_irq arch/x86/kernel/irq.c:233 [inline]
       __common_interrupt+0xd7/0x1e0 arch/x86/kernel/irq.c:252
       common_interrupt+0xb0/0xd0 arch/x86/kernel/irq.c:242
       asm_common_interrupt+0x22/0x40 arch/x86/include/asm/idtentry.h:667
       __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:161 [inline]
       _raw_spin_unlock_irqrestore+0xbc/0x120 kernel/locking/spinlock.c:194
       spin_unlock_irqrestore include/linux/spinlock.h:419 [inline]
       uart_write+0x62f/0x880 drivers/tty/serial/serial_core.c:592
       process_output_block drivers/tty/n_tty.c:592 [inline]
       n_tty_write+0xd2e/0x1210 drivers/tty/n_tty.c:2339
       do_tty_write drivers/tty/tty_io.c:1038 [inline]
       file_tty_write+0x557/0x910 drivers/tty/tty_io.c:1110
       call_write_iter include/linux/fs.h:2173 [inline]
       new_sync_write fs/read_write.c:507 [inline]
       vfs_write+0x745/0xd60 fs/read_write.c:594
       ksys_write+0x152/0x260 fs/read_write.c:647
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

-> #1 (&port_lock_key){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0xb0/0x100 kernel/locking/spinlock.c:162
       serial8250_console_write+0x178/0x1000 drivers/tty/serial/8250/8250_port.c:3368
       call_console_drivers kernel/printk/printk.c:-1 [inline]
       console_unlock+0xb9a/0x1120 kernel/printk/printk.c:2744
       vprintk_emit+0xc0/0x150 kernel/printk/printk.c:2274
       _printk+0xda/0x130 kernel/printk/printk.c:2299
       register_console+0x699/0x980 kernel/printk/printk.c:3107
       univ8250_console_init+0x41/0x50 drivers/tty/serial/8250/8250_core.c:690
       console_init+0x177/0x5d0 kernel/printk/printk.c:3207
       start_kernel+0x2fc/0x540 init/main.c:1090
       secondary_startup_64_no_verify+0xb1/0xbb

-> #0 (console_owner){-.-.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
       lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
       console_lock_spinning_enable+0x51/0x60 kernel/printk/printk.c:1805
       console_unlock+0x8b6/0x1120 kernel/printk/printk.c:2741
       vprintk_emit+0xc0/0x150 kernel/printk/printk.c:2274
       _printk+0xda/0x130 kernel/printk/printk.c:2299
       fail_dump lib/fault-inject.c:45 [inline]
       should_fail+0x36d/0x4c0 lib/fault-inject.c:146
       should_failslab+0x5/0x20 mm/slab_common.c:1350
       slab_pre_alloc_hook+0x51/0xc0 mm/slab.h:494
       slab_alloc_node mm/slub.c:3139 [inline]
       slab_alloc mm/slub.c:3233 [inline]
       __kmalloc+0x6b/0x330 mm/slub.c:4408
       kmalloc include/linux/slab.h:612 [inline]
       tty_buffer_alloc drivers/tty/tty_buffer.c:177 [inline]
       __tty_buffer_request_room+0x1dd/0x500 drivers/tty/tty_buffer.c:276
       tty_insert_flip_string_fixed_flag drivers/tty/tty_buffer.c:322 [inline]
       tty_insert_flip_string include/linux/tty_flip.h:41 [inline]
       tty_insert_flip_string_and_push_buffer+0x7e/0x370 drivers/tty/tty_buffer.c:586
       ppp_async_push+0x2e1/0x1c80 drivers/net/ppp/ppp_async.c:676
       ppp_async_send+0xc8/0xf0 drivers/net/ppp/ppp_async.c:644
       __ppp_channel_push+0xe8/0x1a0 drivers/net/ppp/ppp_generic.c:2179
       ppp_channel_push+0x18a/0x210 drivers/net/ppp/ppp_generic.c:2206
       ppp_write+0x2a8/0x3d0 drivers/net/ppp/ppp_generic.c:549
       do_loop_readv_writev fs/read_write.c:-1 [inline]
       do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
       vfs_writev fs/read_write.c:928 [inline]
       do_writev+0x281/0x480 fs/read_write.c:971
       do_syscall_x64 arch/x86/entry/common.c:50 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
       entry_SYSCALL_64_after_hwframe+0x66/0xd0

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 ***

5 locks held by syz.0.568/6665:
 #0: ffff88802653ea40 (&pch->upl){++..}-{2:2}, at: ppp_channel_push+0x2c/0x210 drivers/net/ppp/ppp_generic.c:2200
 #1: ffff88802653e9e0 (&pch->downl){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:364 [inline]
 #1: ffff88802653e9e0 (&pch->downl){+...}-{2:2}, at: __ppp_channel_push+0x31/0x1a0 drivers/net/ppp/ppp_generic.c:2175
 #2: ffff888077488030 (&ap->xmit_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:369 [inline]
 #2: ffff888077488030 (&ap->xmit_lock){+...}-{2:2}, at: ppp_async_push+0x8e/0x1c80 drivers/net/ppp/ppp_async.c:669
 #3: ffff88802392a158 (&port->lock){-...}-{2:2}, at: tty_insert_flip_string_and_push_buffer+0x39/0x370 drivers/tty/tty_buffer.c:585
 #4: ffffffff8c313660 (console_lock){+.+.}-{0:0}, at: vprintk_emit+0xa7/0x150 kernel/printk/printk.c:2273

stack backtrace:
CPU: 0 PID: 6665 Comm: syz.0.568 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 check_noncircular+0x296/0x330 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x2c42/0x7d10 kernel/locking/lockdep.c:5012
 lock_acquire+0x19e/0x400 kernel/locking/lockdep.c:5623
 console_lock_spinning_enable+0x51/0x60 kernel/printk/printk.c:1805
 console_unlock+0x8b6/0x1120 kernel/printk/printk.c:2741
 vprintk_emit+0xc0/0x150 kernel/printk/printk.c:2274
 _printk+0xda/0x130 kernel/printk/printk.c:2299
 fail_dump lib/fault-inject.c:45 [inline]
 should_fail+0x36d/0x4c0 lib/fault-inject.c:146
 should_failslab+0x5/0x20 mm/slab_common.c:1350
 slab_pre_alloc_hook+0x51/0xc0 mm/slab.h:494
 slab_alloc_node mm/slub.c:3139 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x6b/0x330 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 tty_buffer_alloc drivers/tty/tty_buffer.c:177 [inline]
 __tty_buffer_request_room+0x1dd/0x500 drivers/tty/tty_buffer.c:276
 tty_insert_flip_string_fixed_flag drivers/tty/tty_buffer.c:322 [inline]
 tty_insert_flip_string include/linux/tty_flip.h:41 [inline]
 tty_insert_flip_string_and_push_buffer+0x7e/0x370 drivers/tty/tty_buffer.c:586
 ppp_async_push+0x2e1/0x1c80 drivers/net/ppp/ppp_async.c:676
 ppp_async_send+0xc8/0xf0 drivers/net/ppp/ppp_async.c:644
 __ppp_channel_push+0xe8/0x1a0 drivers/net/ppp/ppp_generic.c:2179
 ppp_channel_push+0x18a/0x210 drivers/net/ppp/ppp_generic.c:2206
 ppp_write+0x2a8/0x3d0 drivers/net/ppp/ppp_generic.c:549
 do_loop_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
 vfs_writev fs/read_write.c:928 [inline]
 do_writev+0x281/0x480 fs/read_write.c:971
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f5d9caaee59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5d9ad08028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f5d9cd27fa0 RCX: 00007f5d9caaee59
RDX: 0000000000000001 RSI: 0000200000000440 RDI: 0000000000000005
RBP: 00007f5d9ad08090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f5d9cd28038 R14: 00007f5d9cd27fa0 R15: 00007ffdec4f5418
 </TASK>
CPU: 0 PID: 6665 Comm: syz.0.568 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 fail_dump lib/fault-inject.c:52 [inline]
 should_fail+0x38c/0x4c0 lib/fault-inject.c:146
 should_failslab+0x5/0x20 mm/slab_common.c:1350
 slab_pre_alloc_hook+0x51/0xc0 mm/slab.h:494
 slab_alloc_node mm/slub.c:3139 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 __kmalloc+0x6b/0x330 mm/slub.c:4408
 kmalloc include/linux/slab.h:612 [inline]
 tty_buffer_alloc drivers/tty/tty_buffer.c:177 [inline]
 __tty_buffer_request_room+0x1dd/0x500 drivers/tty/tty_buffer.c:276
 tty_insert_flip_string_fixed_flag drivers/tty/tty_buffer.c:322 [inline]
 tty_insert_flip_string include/linux/tty_flip.h:41 [inline]
 tty_insert_flip_string_and_push_buffer+0x7e/0x370 drivers/tty/tty_buffer.c:586
 ppp_async_push+0x2e1/0x1c80 drivers/net/ppp/ppp_async.c:676
 ppp_async_send+0xc8/0xf0 drivers/net/ppp/ppp_async.c:644
 __ppp_channel_push+0xe8/0x1a0 drivers/net/ppp/ppp_generic.c:2179
 ppp_channel_push+0x18a/0x210 drivers/net/ppp/ppp_generic.c:2206
 ppp_write+0x2a8/0x3d0 drivers/net/ppp/ppp_generic.c:549
 do_loop_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x3e4/0x7b0 fs/read_write.c:857
 vfs_writev fs/read_write.c:928 [inline]
 do_writev+0x281/0x480 fs/read_write.c:971
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f5d9caaee59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5d9ad08028 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f5d9cd27fa0 RCX: 00007f5d9caaee59
RDX: 0000000000000001 RSI: 0000200000000440 RDI: 0000000000000005
RBP: 00007f5d9ad08090 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007f5d9cd28038 R14: 00007f5d9cd27fa0 R15: 00007ffdec4f5418
 </TASK>