rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	2-....: (1 GPs behind) idle=7c34/1/0x4000000000000000 softirq=29953/29955 fqs=5116
rcu: 	         hardirqs   softirqs   csw/system
rcu: 	 number:     5263          0            0
rcu: 	cputime:      190          0        52308   ==> 52510(ms)
rcu: 	(t=10502 jiffies g=32293 q=7986 ncpus=4)
CPU: 2 UID: 0 PID: 1421 Comm: aoe_tx0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x31/0x80 kernel/locking/spinlock.c:194
Code: f5 53 48 8b 74 24 10 48 89 fb 48 83 c7 18 e8 a6 cb 6b f6 48 89 df e8 8e 19 6c f6 f7 c5 00 02 00 00 75 23 9c 58 f6 c4 02 75 37 <bf> 01 00 00 00 e8 15 62 5c f6 65 8b 05 3e ea 6c 08 85 c0 74 16 5b
RSP: 0018:ffffc90007bcf908 EFLAGS: 00000246
RAX: 0000000000000002 RBX: ffffffff9b1f0d60 RCX: 0000000000000004
RDX: 0000000000000000 RSI: ffffffff8dc4131b RDI: ffffffff8bfa32a0
RBP: 0000000000000293 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffffffff8f2fc100
R13: ffffffff9b1f0e68 R14: 0000000000000000 R15: ffffffff9b1f0ea0
FS:  0000000000000000(0000) GS:ffff8880975e5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f9617d4beb8 CR3: 0000000028fda000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
 uart_port_unlock_irqrestore include/linux/serial_core.h:788 [inline]
 uart_port_unlock_deref drivers/tty/serial/serial_core.c:91 [inline]
 uart_port_unlock_deref drivers/tty/serial/serial_core.c:88 [inline]
 uart_write_room+0x2d2/0x930 drivers/tty/serial/serial_core.c:647
 tty_write_room+0x66/0x90 drivers/tty/tty_ioctl.c:69
 handle_tx+0x14a/0x620 drivers/net/caif/caif_serial.c:212
 __netdev_start_xmit include/linux/netdevice.h:5273 [inline]
 netdev_start_xmit include/linux/netdevice.h:5282 [inline]
 xmit_one net/core/dev.c:3866 [inline]
 dev_hard_start_xmit+0x127/0x6c0 net/core/dev.c:3882
 __dev_queue_xmit+0x6dd/0x46f0 net/core/dev.c:4832
 dev_queue_xmit include/linux/netdevice.h:3381 [inline]
 tx+0xc4/0x130 drivers/block/aoe/aoenet.c:62
 kthread+0x1d8/0x3c0 drivers/block/aoe/aoecmd.c:1241
 kthread+0x3b3/0x730 kernel/kthread.c:463
 ret_from_fork+0x754/0xaf0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>