syzbot

INFO: rcu_sched self-detected stall on CPU
	0-....: (124999 ticks this GP) idle=73e/140000000000001/0 softirq=18574/18574 fqs=31222 
	 (t=125000 jiffies g=10072 c=10071 q=407)
NMI backtrace for cpu 0
CPU: 0 PID: 7724 Comm: syz-executor0 Not tainted 4.15.0-rc5+ #240
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103
 nmi_trigger_cpumask_backtrace+0x122/0x180 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:156 [inline]
 rcu_dump_cpu_stacks+0x186/0x1d9 kernel/rcu/tree.c:1459
 print_cpu_stall kernel/rcu/tree.c:1608 [inline]
 check_cpu_stall.isra.61+0xbb8/0x15b0 kernel/rcu/tree.c:1676
 __rcu_pending kernel/rcu/tree.c:3440 [inline]
 rcu_pending kernel/rcu/tree.c:3502 [inline]
 rcu_check_callbacks+0x256/0xd00 kernel/rcu/tree.c:2842
 update_process_times+0x30/0x60 kernel/time/timer.c:1630
 tick_sched_handle+0x85/0x160 kernel/time/tick-sched.c:162
 tick_sched_timer+0x42/0x120 kernel/time/tick-sched.c:1166
 __run_hrtimer kernel/time/hrtimer.c:1211 [inline]
 __hrtimer_run_queues+0x358/0xe20 kernel/time/hrtimer.c:1275
 hrtimer_interrupt+0x1c2/0x5e0 kernel/time/hrtimer.c:1309
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1025 [inline]
 smp_apic_timer_interrupt+0x14a/0x700 arch/x86/kernel/apic/apic.c:1050
 apic_timer_interrupt+0xa9/0xb0 arch/x86/entry/entry_64.S:904
 </IRQ>
RIP: 0010:__read_once_size include/linux/compiler.h:183 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x3b/0x50 kernel/kcov.c:106
RSP: 0018:ffff8801bdeefb38 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff11
RAX: 0000000000010000 RBX: ffffc900012d8060 RCX: ffffffff8286ff66
RDX: 000000000000ffff RSI: ffffc900029d0000 RDI: ffffc900012d9260
RBP: ffff8801bdeefb38 R08: 1ffff10037bdde99 R09: 0000000000000004
R10: ffff8801bdeef988 R11: 0000000000000003 R12: ffffc900012d7000
R13: 0000000455ddca44 R14: 0000000020dd9000 R15: ffff8801d6790bf8
 inq_canon drivers/tty/n_tty.c:2412 [inline]
 n_tty_ioctl+0x266/0x2d0 drivers/tty/n_tty.c:2429
 tty_ioctl+0x336/0x1610 drivers/tty/tty_io.c:2638
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452ac9
RSP: 002b:00007f49bdc2fc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
RDX: 0000000020dd9000 RSI: 000000000000541b RDI: 0000000000000014
RBP: 00000000000005c0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f5aa0
R13: 00000000ffffffff R14: 00007f49bdc306d4 R15: 0000000000000000