[syzbot] [hams?] possible deadlock in serial8250_console_write

From: syzbot
Date: Tue Apr 02 2024 - 13:32:55 EST

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Hello,

syzbot found the following issue on:

HEAD commit: fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17277dd9180000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d90a36f0cab495a
dashboard link: https://syzkaller.appspot.com/bug?extid=8e03da5d64bc85098811
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f6c04726a2ae/disk-fe46a7dd.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/09c26ce901ea/vmlinux-fe46a7dd.xz
kernel image: https://storage.googleapis.com/syzbot-assets/134acf7f5322/bzImage-fe46a7dd.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8e03da5d64bc85098811@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
WARNING: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected
6.8.0-syzkaller-08951-gfe46a7dd189e #0 Not tainted
-----------------------------------------------------
kworker/u8:0/10 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
ffffffff8ec014f8 (disc_data_lock#2){.+.+}-{2:2}, at: sp_get drivers/net/hamradio/6pack.c:376 [inline]
ffffffff8ec014f8 (disc_data_lock#2){.+.+}-{2:2}, at: sixpack_write_wakeup+0x30/0x430 drivers/net/hamradio/6pack.c:397

and this task is already holding:
ffffffff947d1df8 (&port_lock_key){-.-.}-{2:2}, at: uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
ffffffff947d1df8 (&port_lock_key){-.-.}-{2:2}, at: uart_write+0x101/0x5c0 drivers/tty/serial/serial_core.c:595
which would create a new lock dependency:
(&port_lock_key){-.-.}-{2:2} -> (disc_data_lock#2){.+.+}-{2:2}

but this new dependency connects a HARDIRQ-irq-safe lock:
(&port_lock_key){-.-.}-{2:2}

.. which became HARDIRQ-irq-safe at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
serial8250_console_write+0x1a8/0x1840 drivers/tty/serial/8250/8250_port.c:3403
console_emit_next_record kernel/printk/printk.c:2907 [inline]
console_flush_all+0x865/0xfd0 kernel/printk/printk.c:2973
console_unlock+0x13b/0x4d0 kernel/printk/printk.c:3042
vprintk_emit+0x5a6/0x770 kernel/printk/printk.c:2342
_printk+0xd5/0x120 kernel/printk/printk.c:2367
vkms_vblank_simulate+0x2f8/0x360 drivers/gpu/drm/vkms/vkms_crtc.c:26
__run_hrtimer kernel/time/hrtimer.c:1692 [inline]
__hrtimer_run_queues+0x595/0xd00 kernel/time/hrtimer.c:1756
hrtimer_interrupt+0x396/0x990 kernel/time/hrtimer.c:1818
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1032 [inline]
__sysvec_apic_timer_interrupt+0x107/0x3a0 arch/x86/kernel/apic/apic.c:1049
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1043
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
__outl arch/x86/include/asm/shared/io.h:24 [inline]
iowrite32+0x35/0x90 lib/iomap.c:225
setup_vq+0x166/0x2d0 drivers/virtio/virtio_pci_legacy.c:150
vp_setup_vq+0xbf/0x330 drivers/virtio/virtio_pci_common.c:189
vp_find_vqs_msix+0x8b2/0xc80 drivers/virtio/virtio_pci_common.c:331
vp_find_vqs+0x4c/0x4e0 drivers/virtio/virtio_pci_common.c:408
virtio_find_vqs_ctx include/linux/virtio_config.h:242 [inline]
virtnet_find_vqs drivers/net/virtio_net.c:4347 [inline]
init_vqs+0xcdb/0x15d0 drivers/net/virtio_net.c:4436
virtnet_probe+0x1988/0x3850 drivers/net/virtio_net.c:4756
virtio_dev_probe+0x991/0xaf0 drivers/virtio/virtio.c:311
really_probe+0x29e/0xc50 drivers/base/dd.c:658
__driver_probe_device+0x1a2/0x3e0 drivers/base/dd.c:800
driver_probe_device+0x50/0x430 drivers/base/dd.c:830
__driver_attach+0x45f/0x710 drivers/base/dd.c:1216
bus_for_each_dev+0x239/0x2b0 drivers/base/bus.c:368
bus_add_driver+0x347/0x620 drivers/base/bus.c:673
driver_register+0x23a/0x320 drivers/base/driver.c:246
virtio_net_driver_init+0x92/0xe0 drivers/net/virtio_net.c:5003
do_one_initcall+0x238/0x830 init/main.c:1241
do_initcall_level+0x157/0x210 init/main.c:1303
do_initcalls+0x3f/0x80 init/main.c:1319
kernel_init_freeable+0x435/0x5d0 init/main.c:1550
kernel_init+0x1d/0x2a0 init/main.c:1439
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

to a HARDIRQ-irq-unsafe lock:
(disc_data_lock#2){.+.+}-{2:2}

.. which became HARDIRQ-irq-unsafe at:
..
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_receive_buf+0x56/0x1380 drivers/net/hamradio/6pack.c:439
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

other info that might help us debug this:

Possible interrupt unsafe locking scenario:

CPU0 CPU1
---- ----
lock(disc_data_lock#2);
local_irq_disable();
lock(&port_lock_key);
lock(disc_data_lock#2);
<Interrupt>
lock(&port_lock_key);

*** DEADLOCK ***

6 locks held by kworker/u8:0/10:
#0: ffff888014c81148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3229 [inline]
#0: ffff888014c81148 ((wq_completion)events_unbound){+.+.}-{0:0}, at: process_scheduled_works+0x8e0/0x1770 kernel/workqueue.c:3335
#1: ffffc900000f7d00 ((work_completion)(&buf->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3230 [inline]
#1: ffffc900000f7d00 ((work_completion)(&buf->work)){+.+.}-{0:0}, at: process_scheduled_works+0x91b/0x1770 kernel/workqueue.c:3335
#2: ffff88801f660ce8 (&buf->lock){+.+.}-{3:3}, at: flush_to_ldisc+0x38/0x860 drivers/tty/tty_buffer.c:466
#3: ffff88802ca5c0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x1c/0x80 drivers/tty/tty_ldisc.c:263
#4: ffffffff947d1df8 (&port_lock_key){-.-.}-{2:2}, at: uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
#4: ffffffff947d1df8 (&port_lock_key){-.-.}-{2:2}, at: uart_write+0x101/0x5c0 drivers/tty/serial/serial_core.c:595
#5: ffff88802ca5c0a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref+0x1c/0x80 drivers/tty/tty_ldisc.c:263

the dependencies between HARDIRQ-irq-safe lock and the holding lock:
-> (&port_lock_key){-.-.}-{2:2} {
IN-HARDIRQ-W at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
serial8250_console_write+0x1a8/0x1840 drivers/tty/serial/8250/8250_port.c:3403
console_emit_next_record kernel/printk/printk.c:2907 [inline]
console_flush_all+0x865/0xfd0 kernel/printk/printk.c:2973
console_unlock+0x13b/0x4d0 kernel/printk/printk.c:3042
vprintk_emit+0x5a6/0x770 kernel/printk/printk.c:2342
_printk+0xd5/0x120 kernel/printk/printk.c:2367
vkms_vblank_simulate+0x2f8/0x360 drivers/gpu/drm/vkms/vkms_crtc.c:26
__run_hrtimer kernel/time/hrtimer.c:1692 [inline]
__hrtimer_run_queues+0x595/0xd00 kernel/time/hrtimer.c:1756
hrtimer_interrupt+0x396/0x990 kernel/time/hrtimer.c:1818
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1032 [inline]
__sysvec_apic_timer_interrupt+0x107/0x3a0 arch/x86/kernel/apic/apic.c:1049
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1043 [inline]
sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1043
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
__outl arch/x86/include/asm/shared/io.h:24 [inline]
iowrite32+0x35/0x90 lib/iomap.c:225
setup_vq+0x166/0x2d0 drivers/virtio/virtio_pci_legacy.c:150
vp_setup_vq+0xbf/0x330 drivers/virtio/virtio_pci_common.c:189
vp_find_vqs_msix+0x8b2/0xc80 drivers/virtio/virtio_pci_common.c:331
vp_find_vqs+0x4c/0x4e0 drivers/virtio/virtio_pci_common.c:408
virtio_find_vqs_ctx include/linux/virtio_config.h:242 [inline]
virtnet_find_vqs drivers/net/virtio_net.c:4347 [inline]
init_vqs+0xcdb/0x15d0 drivers/net/virtio_net.c:4436
virtnet_probe+0x1988/0x3850 drivers/net/virtio_net.c:4756
virtio_dev_probe+0x991/0xaf0 drivers/virtio/virtio.c:311
really_probe+0x29e/0xc50 drivers/base/dd.c:658
__driver_probe_device+0x1a2/0x3e0 drivers/base/dd.c:800
driver_probe_device+0x50/0x430 drivers/base/dd.c:830
__driver_attach+0x45f/0x710 drivers/base/dd.c:1216
bus_for_each_dev+0x239/0x2b0 drivers/base/bus.c:368
bus_add_driver+0x347/0x620 drivers/base/bus.c:673
driver_register+0x23a/0x320 drivers/base/driver.c:246
virtio_net_driver_init+0x92/0xe0 drivers/net/virtio_net.c:5003
do_one_initcall+0x238/0x830 init/main.c:1241
do_initcall_level+0x157/0x210 init/main.c:1303
do_initcalls+0x3f/0x80 init/main.c:1319
kernel_init_freeable+0x435/0x5d0 init/main.c:1550
kernel_init+0x1d/0x2a0 init/main.c:1439
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
IN-SOFTIRQ-W at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
serial8250_console_write+0x1a8/0x1840 drivers/tty/serial/8250/8250_port.c:3403
console_emit_next_record kernel/printk/printk.c:2907 [inline]
console_flush_all+0x865/0xfd0 kernel/printk/printk.c:2973
console_unlock+0x13b/0x4d0 kernel/printk/printk.c:3042
vprintk_emit+0x5a6/0x770 kernel/printk/printk.c:2342
_printk+0xd5/0x120 kernel/printk/printk.c:2367
ip_frag_reasm net/ipv4/ip_fragment.c:476 [inline]
ip_frag_queue net/ipv4/ip_fragment.c:379 [inline]
ip_defrag+0x1bc6/0x26b0 net/ipv4/ip_fragment.c:499
nf_ct_ipv4_gather_frags net/ipv4/netfilter/nf_defrag_ipv4.c:32 [inline]
ipv4_conntrack_defrag+0x3de/0x5a0 net/ipv4/netfilter/nf_defrag_ipv4.c:87
nf_hook_entry_hookfn include/linux/netfilter.h:154 [inline]
nf_hook_slow+0xc3/0x220 net/netfilter/core.c:626
nf_hook include/linux/netfilter.h:269 [inline]
NF_HOOK+0x29e/0x450 include/linux/netfilter.h:312
__netif_receive_skb_one_core net/core/dev.c:5538 [inline]
__netif_receive_skb+0x2bf/0x6a0 net/core/dev.c:5652
process_backlog+0x39d/0x7a0 net/core/dev.c:5981
__napi_poll+0xcb/0x490 net/core/dev.c:6632
napi_poll net/core/dev.c:6701 [inline]
net_rx_action+0x7bb/0x1090 net/core/dev.c:6813
__do_softirq+0x2bc/0x943 kernel/softirq.c:554
do_softirq+0x11b/0x1e0 kernel/softirq.c:455
__local_bh_enable_ip+0x1bb/0x200 kernel/softirq.c:382
local_bh_enable include/linux/bottom_half.h:33 [inline]
rcu_read_unlock_bh include/linux/rcupdate.h:820 [inline]
__dev_queue_xmit+0x15fd/0x3b10 net/core/dev.c:4362
packet_snd net/packet/af_packet.c:3083 [inline]
packet_sendmsg+0x4932/0x63d0 net/packet/af_packet.c:3115
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg+0x221/0x270 net/socket.c:745
__sys_sendto+0x3a4/0x4f0 net/socket.c:2191
__do_sys_sendto net/socket.c:2203 [inline]
__se_sys_sendto net/socket.c:2199 [inline]
__x64_sys_sendto+0xde/0x100 net/socket.c:2199
do_syscall_64+0xfb/0x240
entry_SYSCALL_64_after_hwframe+0x6d/0x75
INITIAL USE at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xd5/0x120 kernel/locking/spinlock.c:162
uart_port_lock_irqsave include/linux/serial_core.h:616 [inline]
serial8250_do_set_termios+0x531/0x17e0 drivers/tty/serial/8250/8250_port.c:2793
uart_set_options+0x3eb/0x730 drivers/tty/serial/serial_core.c:2320
serial8250_console_setup+0x3db/0x670 drivers/tty/serial/8250/8250_port.c:3507
univ8250_console_setup+0x3ac/0x470 drivers/tty/serial/8250/8250_core.c:632
try_enable_preferred_console+0x40d/0x560 kernel/printk/printk.c:3308
register_console+0x261/0xcd0 kernel/printk/printk.c:3485
univ8250_console_init+0x49/0x50 drivers/tty/serial/8250/8250_core.c:717
console_init+0x198/0x680 kernel/printk/printk.c:3694
start_kernel+0x2d3/0x500 init/main.c:1012
x86_64_start_reservations+0x2a/0x30 arch/x86/kernel/head64.c:509
x86_64_start_kernel+0x99/0xa0 arch/x86/kernel/head64.c:490
common_startup_64+0x13e/0x147
}
... key at: [<ffffffff947d1200>] port_lock_key+0x0/0x20

the dependencies between the lock to be acquired
and HARDIRQ-irq-unsafe lock:
-> (disc_data_lock#2){.+.+}-{2:2} {
HARDIRQ-ON-R at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_receive_buf+0x56/0x1380 drivers/net/hamradio/6pack.c:439
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
SOFTIRQ-ON-R at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_receive_buf+0x56/0x1380 drivers/net/hamradio/6pack.c:439
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
INITIAL READ USE at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_receive_buf+0x56/0x1380 drivers/net/hamradio/6pack.c:439
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
}
... key at: [<ffffffff8ec014f8>] disc_data_lock+0x18/0x100
... acquired at:
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_write_wakeup+0x30/0x430 drivers/net/hamradio/6pack.c:397
tty_wakeup+0xbb/0x100 drivers/tty/tty_io.c:523
tty_port_default_wakeup+0xa6/0xf0 drivers/tty/tty_port.c:69
serial8250_tx_chars+0x6ad/0x8a0 drivers/tty/serial/8250/8250_port.c:1835
__start_tx+0x32e/0x470 drivers/tty/serial/8250/8250_port.c:1544
__uart_start+0x2d6/0x3c0 drivers/tty/serial/serial_core.c:160
uart_write+0x427/0x5c0 drivers/tty/serial/serial_core.c:615
decode_prio_command drivers/net/hamradio/6pack.c:888 [inline]
sixpack_decode drivers/net/hamradio/6pack.c:963 [inline]
sixpack_receive_buf+0x427/0x1380 drivers/net/hamradio/6pack.c:453
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243

stack backtrace:
CPU: 0 PID: 10 Comm: kworker/u8:0 Not tainted 6.8.0-syzkaller-08951-gfe46a7dd189e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Workqueue: events_unbound flush_to_ldisc
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
print_bad_irq_dependency kernel/locking/lockdep.c:2626 [inline]
check_irq_usage kernel/locking/lockdep.c:2865 [inline]
check_prev_add kernel/locking/lockdep.c:3138 [inline]
check_prevs_add kernel/locking/lockdep.c:3253 [inline]
validate_chain+0x4dc7/0x58e0 kernel/locking/lockdep.c:3869
__lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
lock_acquire+0x1e4/0x530 kernel/locking/lockdep.c:5754
__raw_read_lock include/linux/rwlock_api_smp.h:150 [inline]
_raw_read_lock+0x36/0x50 kernel/locking/spinlock.c:228
sp_get drivers/net/hamradio/6pack.c:376 [inline]
sixpack_write_wakeup+0x30/0x430 drivers/net/hamradio/6pack.c:397
tty_wakeup+0xbb/0x100 drivers/tty/tty_io.c:523
tty_port_default_wakeup+0xa6/0xf0 drivers/tty/tty_port.c:69
serial8250_tx_chars+0x6ad/0x8a0 drivers/tty/serial/8250/8250_port.c:1835
__start_tx+0x32e/0x470 drivers/tty/serial/8250/8250_port.c:1544
__uart_start+0x2d6/0x3c0 drivers/tty/serial/serial_core.c:160
uart_write+0x427/0x5c0 drivers/tty/serial/serial_core.c:615
decode_prio_command drivers/net/hamradio/6pack.c:888 [inline]
sixpack_decode drivers/net/hamradio/6pack.c:963 [inline]
sixpack_receive_buf+0x427/0x1380 drivers/net/hamradio/6pack.c:453
tty_ldisc_receive_buf+0x11f/0x170 drivers/tty/tty_buffer.c:390
tty_port_default_receive_buf+0x6d/0xa0 drivers/tty/tty_port.c:37
receive_buf drivers/tty/tty_buffer.c:444 [inline]
flush_to_ldisc+0x328/0x860 drivers/tty/tty_buffer.c:494
process_one_work kernel/workqueue.c:3254 [inline]
process_scheduled_works+0xa00/0x1770 kernel/workqueue.c:3335
worker_thread+0x86d/0xd70 kernel/workqueue.c:3416
kthread+0x2f0/0x390 kernel/kthread.c:388
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:243
</TASK>

---
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