INFO: rcu detected stall in dev_ioctl

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6b8a7946 Merge tag 'for_linus' of git://git.kernel.org/pub..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175973cee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4737c15fc47048f2
dashboard link: https://syzkaller.appspot.com/bug?extid=1a41521b3198c9e15c2f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1a41521b3198c9e15c2f@xxxxxxxxxxxxxxxxxxxxxxxxx

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (1 GPs behind) idle=e6a/1/0x4000000000000002  
softirq=14144/14145 fqs=5200
	(t=10500 jiffies g=14865 q=1519)
NMI backtrace for cpu 1
CPU: 1 PID: 10088 Comm: syz-executor.4 Not tainted 5.4.0-rc8-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x197/0x210 lib/dump_stack.c:118
 nmi_cpu_backtrace.cold+0x70/0xb2 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x23b/0x28b lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:164 [inline]
 rcu_dump_cpu_stacks+0x183/0x1cf kernel/rcu/tree_stall.h:254
 print_cpu_stall kernel/rcu/tree_stall.h:455 [inline]
 check_cpu_stall kernel/rcu/tree_stall.h:529 [inline]
 rcu_pending kernel/rcu/tree.c:2795 [inline]
 rcu_sched_clock_irq.cold+0x4fd/0xc12 kernel/rcu/tree.c:2244
 update_process_times+0x2d/0x70 kernel/time/timer.c:1726
 tick_sched_handle+0xa2/0x190 kernel/time/tick-sched.c:167
 tick_sched_timer+0x53/0x140 kernel/time/tick-sched.c:1299
 __run_hrtimer kernel/time/hrtimer.c:1514 [inline]
 __hrtimer_run_queues+0x364/0xe40 kernel/time/hrtimer.c:1576
 hrtimer_interrupt+0x314/0x770 kernel/time/hrtimer.c:1638
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1110 [inline]
 smp_apic_timer_interrupt+0x160/0x610 arch/x86/kernel/apic/apic.c:1135
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:830
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:756  
[inline]
RIP: 0010:console_unlock+0xbc7/0xf10 kernel/printk/printk.c:2481
Code: f3 88 48 c1 e8 03 42 80 3c 30 00 0f 85 e4 02 00 00 48 83 3d 4a 8f 96  
07 00 0f 84 91 01 00 00 e8 3f c2 16 00 48 8b 7d 98 57 9d <0f> 1f 44 00 00  
e9 6d ff ff ff e8 2a c2 16 00 48 8b 7d 08 c7 05 dc
RSP: 0018:ffff888057b17528 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: 0000000000000200 RCX: ffffc9000e7a9000
RDX: 0000000000040000 RSI: ffffffff815c94e1 RDI: 0000000000000246
RBP: ffff888057b175b0 R08: 1ffffffff14f0134 R09: fffffbfff14f0135
R10: fffffbfff14f0134 R11: ffffffff8a7809a7 R12: 0000000000000000
R13: ffffffff843e6780 R14: dffffc0000000000 R15: ffffffff895db0f0
 vprintk_emit+0x2a0/0x700 kernel/printk/printk.c:1996
 vprintk_default+0x28/0x30 kernel/printk/printk.c:2023
 vprintk_func+0x7e/0x189 kernel/printk/printk_safe.c:386
 printk+0xba/0xed kernel/printk/printk.c:2056
 batadv_tt_local_resize_to_mtu.cold+0x18/0x1e  
net/batman-adv/translation-table.c:4202
 batadv_update_min_mtu net/batman-adv/hard-interface.c:626 [inline]
 batadv_hard_if_event+0x64f/0xfa0 net/batman-adv/hard-interface.c:1056
 notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
 __raw_notifier_call_chain kernel/notifier.c:396 [inline]
 raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
 call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1668
 call_netdevice_notifiers_mtu net/core/dev.c:1717 [inline]
 dev_set_mtu_ext+0x354/0x5a0 net/core/dev.c:8014
 dev_set_mtu+0xa5/0x130 net/core/dev.c:8035
 dev_ifsioc+0x357/0xa00 net/core/dev_ioctl.c:244
 dev_ioctl+0x1b8/0xc70 net/core/dev_ioctl.c:489
 sock_do_ioctl+0x1b7/0x2f0 net/socket.c:1061
 sock_ioctl+0x3ed/0x790 net/socket.c:1189
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:696
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a639
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8b5149ac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a639
RDX: 0000000020000180 RSI: 0000000000008922 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f8b5149b6d4
R13: 00000000004c6652 R14: 00000000004dbae8 R15: 00000000ffffffff


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.