------------[ cut here ]------------
WARNING: CPU: 2 PID: 6590 at drivers/tty/serial/serial_core.c:625 uart_write+0x2bf/0x3e0 drivers/tty/serial/serial_core.c:625
Modules linked in:
CPU: 2 PID: 6590 Comm: syz-executor.3 Not tainted 6.10.0-rc3-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:uart_write+0x2bf/0x3e0 drivers/tty/serial/serial_core.c:625
Code: 6b fc e9 4e ff ff ff e8 5f 14 91 fc 90 0f 0b 90 49 c7 c4 d2 ff ff ff e9 39 ff ff ff e8 4a 14 91 fc 45 31 ff e8 42 14 91 fc 90 <0f> 0b 90 48 85 ed 74 8c e8 34 14 91 fc 4c 8d a5 08 01 00 00 4c 89
RSP: 0018:ffffc900036cfae8 EFLAGS: 00010083
RAX: 000000000000ba5d RBX: ffff88801f860be8 RCX: ffffc90008fc1000
RDX: 0000000000040000 RSI: ffffffff84fcd10e RDI: ffff88801f860f48
RBP: ffffffff94de0f60 R08: 0000000000000001 R09: fffff520006d9f4b
R10: 0000000000000003 R11: ffffffff939364d8 R12: 0000000000000001
R13: 000000000000017a R14: ffff88801f2e8001 R15: 0000000000000287

======================================================
WARNING: possible circular locking dependency detected
6.10.0-rc3-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.3/6590 is trying to acquire lock:
ffffffff8dabeee0 (console_owner){-.-.}-{0:0}, at: console_trylock_spinning kernel/printk/printk.c:1994 [inline]
ffffffff8dabeee0 (console_owner){-.-.}-{0:0}, at: vprintk_emit kernel/printk/printk.c:2344 [inline]
ffffffff8dabeee0 (console_owner){-.-.}-{0:0}, at: vprintk_emit+0x42d/0x5a0 kernel/printk/printk.c:2300

but task is already holding lock:
ffffffff94de0f78 (&port_lock_key){-.-.}-{2:2}, at: uart_port_lock_irqsave include/linux/serial_core.h:618 [inline]
ffffffff94de0f78 (&port_lock_key){-.-.}-{2:2}, at: uart_write+0x134/0x3e0 drivers/tty/serial/serial_core.c:624

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&port_lock_key){-.-.}-{2:2}:
       __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
       _raw_spin_lock_irqsave+0x3a/0x60 kernel/locking/spinlock.c:162
       uart_port_lock_irqsave include/linux/serial_core.h:618 [inline]
       serial8250_console_write+0xaa6/0x1090 drivers/tty/serial/8250/8250_port.c:3352
       console_emit_next_record kernel/printk/printk.c:2928 [inline]
       console_flush_all+0x53f/0xd70 kernel/printk/printk.c:2994
       console_unlock+0xae/0x290 kernel/printk/printk.c:3063
       vprintk_emit kernel/printk/printk.c:2345 [inline]
       vprintk_emit+0x11a/0x5a0 kernel/printk/printk.c:2300
       vprintk+0x7f/0xa0 kernel/printk/printk_safe.c:45
       _printk+0xc8/0x100 kernel/printk/printk.c:2370
       register_console+0xa88/0x10a0 kernel/printk/printk.c:3596
       univ8250_console_init+0x35/0x50 drivers/tty/serial/8250/8250_core.c:719
       console_init+0xcc/0x680 kernel/printk/printk.c:3742
       start_kernel+0x295/0x4c0 init/main.c:1038
       x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:507
       x86_64_start_kernel+0xb2/0xc0 arch/x86/kernel/head64.c:488
       common_startup_64+0x13e/0x148

-> #0 (console_owner){-.-.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
       lock_acquire kernel/locking/lockdep.c:5754 [inline]
       lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5719
       console_trylock_spinning kernel/printk/printk.c:1994 [inline]
       vprintk_emit kernel/printk/printk.c:2344 [inline]
       vprintk_emit+0x442/0x5a0 kernel/printk/printk.c:2300
       vprintk+0x7f/0xa0 kernel/printk/printk_safe.c:45
       _printk+0xc8/0x100 kernel/printk/printk.c:2370
       __show_regs+0x2d3/0x750 arch/x86/kernel/process_64.c:91
       show_regs+0x4f/0xa0 arch/x86/kernel/dumpstack.c:472
       __warn+0xe5/0x3c0 kernel/panic.c:691
       __report_bug lib/bug.c:199 [inline]
       report_bug+0x3c0/0x580 lib/bug.c:219
       handle_bug+0x3d/0x70 arch/x86/kernel/traps.c:239
       exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:260
       asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:621
       uart_write+0x2bf/0x3e0 drivers/tty/serial/serial_core.c:625
       ppp_async_push+0x89e/0x1740 drivers/net/ppp/ppp_async.c:666
       ppp_async_send+0xe5/0x120 drivers/net/ppp/ppp_async.c:634
       __ppp_channel_push+0xe5/0x230 drivers/net/ppp/ppp_generic.c:2150
       ppp_channel_push+0x1c2/0x250 drivers/net/ppp/ppp_generic.c:2177
       ppp_write+0x236/0x2e0 drivers/net/ppp/ppp_generic.c:525
       vfs_write+0x29a/0x1140 fs/read_write.c:588
       ksys_write+0x12f/0x260 fs/read_write.c:643
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

4 locks held by syz-executor.3/6590:
 #0: ffff888022798248 (&pch->upl){.+..}-{2:2}, at: ppp_channel_push+0x28/0x250 drivers/net/ppp/ppp_generic.c:2171
 #1: ffff8880227981e0 (&pch->downl){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #1: ffff8880227981e0 (&pch->downl){+...}-{2:2}, at: __ppp_channel_push+0x2a/0x230 drivers/net/ppp/ppp_generic.c:2146
 #2: ffff88801f2e8030 (&ap->xmit_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #2: ffff88801f2e8030 (&ap->xmit_lock){+...}-{2:2}, at: ppp_async_push+0x106/0x1740 drivers/net/ppp/ppp_async.c:659
 #3: ffffffff94de0f78 (&port_lock_key){-.-.}-{2:2}, at: uart_port_lock_irqsave include/linux/serial_core.h:618 [inline]
 #3: ffffffff94de0f78 (&port_lock_key){-.-.}-{2:2}, at: uart_write+0x134/0x3e0 drivers/tty/serial/serial_core.c:624

stack backtrace:
CPU: 2 PID: 6590 Comm: syz-executor.3 Not tainted 6.10.0-rc3-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:114
 check_noncircular+0x31a/0x400 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x2478/0x3b30 kernel/locking/lockdep.c:5137
 lock_acquire kernel/locking/lockdep.c:5754 [inline]
 lock_acquire+0x1b1/0x560 kernel/locking/lockdep.c:5719
 console_trylock_spinning kernel/printk/printk.c:1994 [inline]
 vprintk_emit kernel/printk/printk.c:2344 [inline]
 vprintk_emit+0x442/0x5a0 kernel/printk/printk.c:2300
 vprintk+0x7f/0xa0 kernel/printk/printk_safe.c:45
 _printk+0xc8/0x100 kernel/printk/printk.c:2370
 __show_regs+0x2d3/0x750 arch/x86/kernel/process_64.c:91
 show_regs+0x4f/0xa0 arch/x86/kernel/dumpstack.c:472
 __warn+0xe5/0x3c0 kernel/panic.c:691
 __report_bug lib/bug.c:199 [inline]
 report_bug+0x3c0/0x580 lib/bug.c:219
 handle_bug+0x3d/0x70 arch/x86/kernel/traps.c:239
 exc_invalid_op+0x17/0x50 arch/x86/kernel/traps.c:260
 asm_exc_invalid_op+0x1a/0x20 arch/x86/include/asm/idtentry.h:621
RIP: 0010:uart_write+0x2bf/0x3e0 drivers/tty/serial/serial_core.c:625
Code: 6b fc e9 4e ff ff ff e8 5f 14 91 fc 90 0f 0b 90 49 c7 c4 d2 ff ff ff e9 39 ff ff ff e8 4a 14 91 fc 45 31 ff e8 42 14 91 fc 90 <0f> 0b 90 48 85 ed 74 8c e8 34 14 91 fc 4c 8d a5 08 01 00 00 4c 89
RSP: 0018:ffffc900036cfae8 EFLAGS: 00010083
RAX: 000000000000ba5d RBX: ffff88801f860be8 RCX: ffffc90008fc1000
RDX: 0000000000040000 RSI: ffffffff84fcd10e RDI: ffff88801f860f48
RBP: ffffffff94de0f60 R08: 0000000000000001 R09: fffff520006d9f4b
R10: 0000000000000003 R11: ffffffff939364d8 R12: 0000000000000001
R13: 000000000000017a R14: ffff88801f2e8001 R15: 0000000000000287
 ppp_async_push+0x89e/0x1740 drivers/net/ppp/ppp_async.c:666
 ppp_async_send+0xe5/0x120 drivers/net/ppp/ppp_async.c:634
 __ppp_channel_push+0xe5/0x230 drivers/net/ppp/ppp_generic.c:2150
 ppp_channel_push+0x1c2/0x250 drivers/net/ppp/ppp_generic.c:2177
 ppp_write+0x236/0x2e0 drivers/net/ppp/ppp_generic.c:525
 vfs_write+0x29a/0x1140 fs/read_write.c:588
 ksys_write+0x12f/0x260 fs/read_write.c:643
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f385ea7cee9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f385f7bd0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f385ebabf80 RCX: 00007f385ea7cee9
RDX: 00000000000000b9 RSI: 0000000020000540 RDI: 0000000000000006
RBP: 00007f385eac949e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f385ebabf80 R15: 00007ffd9e8cf5c8
 </TASK>
FS:  00007f385f7bd6c0(0000) GS:ffff88806b200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f385ead946d CR3: 000000002c252000 CR4: 0000000000350ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 ppp_async_push+0x89e/0x1740 drivers/net/ppp/ppp_async.c:666
 ppp_async_send+0xe5/0x120 drivers/net/ppp/ppp_async.c:634
 __ppp_channel_push+0xe5/0x230 drivers/net/ppp/ppp_generic.c:2150
 ppp_channel_push+0x1c2/0x250 drivers/net/ppp/ppp_generic.c:2177
 ppp_write+0x236/0x2e0 drivers/net/ppp/ppp_generic.c:525
 vfs_write+0x29a/0x1140 fs/read_write.c:588
 ksys_write+0x12f/0x260 fs/read_write.c:643
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f385ea7cee9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f385f7bd0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f385ebabf80 RCX: 00007f385ea7cee9
RDX: 00000000000000b9 RSI: 0000000020000540 RDI: 0000000000000006
RBP: 00007f385eac949e R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f385ebabf80 R15: 00007ffd9e8cf5c8
 </TASK>