Re: INFO: rcu detected stall in tty_ioctl

[Dmitry Vyukov]

On Sat, Dec 23, 2017 at 12:48 AM, syzbot
<bot+4e86372b8cb60e44613ff63e5dd1dcaffa7a4d29@xxxxxxxxxxxxxxxxxxxxxxxxx>
wrote:
> syzkaller has found reproducer for the following crash on
> 37759fa6d0fa9e4d6036d19ac12f555bfc0aeafd
> git://git.cmpxchg.org/linux-mmots.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers


I think this is fixed with:

#syz fix: n_tty: fix EXTPROC vs ICANON interaction with TIOCINQ (aka FIONREAD)



> INFO: rcu_sched self-detected stall on CPU
>         1-...!: (124998 ticks this GP) idle=1aa/1/4611686018427387906
> softirq=6401/6401 fqs=178
>          (t=125000 jiffies g=3233 c=3232 q=384)
> rcu_sched kthread starved for 124263 jiffies! g3233 c3232 f0x0
> RCU_GP_WAIT_FQS(3) ->state=0x0 ->cpu=0
> rcu_sched       R  running task    23272     8      2 0x80000000
> Call Trace:
>  context_switch kernel/sched/core.c:2800 [inline]
>  __schedule+0x8eb/0x2060 kernel/sched/core.c:3376
>  schedule+0xf5/0x430 kernel/sched/core.c:3435
>  schedule_timeout+0x13e/0x6f0 kernel/time/timer.c:1818
>  rcu_gp_kthread+0x9dd/0x18e0 kernel/rcu/tree.c:2231
>  kthread+0x33c/0x400 kernel/kthread.c:238
>  ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:524
> NMI backtrace for cpu 1
> CPU: 1 PID: 3169 Comm: syzkaller626814 Not tainted 4.15.0-rc4-mm1+ #49
> 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+0x186/0x1de kernel/rcu/tree.c:1375
>  print_cpu_stall kernel/rcu/tree.c:1524 [inline]
>  check_cpu_stall.isra.62+0xbb8/0x15b0 kernel/rcu/tree.c:1592
>  __rcu_pending kernel/rcu/tree.c:3362 [inline]
>  rcu_pending kernel/rcu/tree.c:3424 [inline]
>  rcu_check_callbacks+0x238/0xd20 kernel/rcu/tree.c:2764
>  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:1148
>  __run_hrtimer kernel/time/hrtimer.c:1210 [inline]
>  __hrtimer_run_queues+0x358/0xe20 kernel/time/hrtimer.c:1274
>  hrtimer_interrupt+0x1c2/0x5e0 kernel/time/hrtimer.c:1308
>  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:920
>  </IRQ>
> RIP: 0010:variable_test_bit arch/x86/include/asm/bitops.h:332 [inline]
> RIP: 0010:inq_canon drivers/tty/n_tty.c:2409 [inline]
> RIP: 0010:n_tty_ioctl+0x218/0x2d0 drivers/tty/n_tty.c:2429
> RSP: 0018:ffff8801c914fb48 EFLAGS: 00000202 ORIG_RAX: ffffffffffffff11
> RAX: 0000000000000643 RBX: ffffc900018c3060 RCX: ffffffff8293be5c
> RDX: 0000000000000000 RSI: 00000000749d30db RDI: ffffc900018c4260
> RBP: ffff8801c914fb88 R08: 1ffff10039229e99 R09: 0000000000000004
> R10: ffff8801c914f988 R11: 0000000000000003 R12: ffffc900018c2000
> R13: 00000002e0efd643 R14: 0000000020a6bffc R15: ffff8801c8493938
>  tty_ioctl+0x336/0x1610 drivers/tty/tty_io.c:2640
>  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: 0033:0x445b39
> RSP: 002b:00007f6ed1479d18 EFLAGS: 00000293 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000006dac3c RCX: 0000000000445b39
> RDX: 0000000020a6bffc RSI: 000000000000541b RDI: 0000000000000013
> RBP: 00000000006dac38 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000293 R12: 6d74702f7665642f
> R13: 00007ffe16e1657f R14: 00007f6ed147a9c0 R15: 0000000000000008
>
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