INFO: rcu detected stall in snd_seq_write

[syzbot <syzbot+97aae04ce27e39cbfca9@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    e27bc174c9c6 Add linux-next specific files for 20180824
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16e0823e400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=28446088176757ea
dashboard link: https://syzkaller.appspot.com/bug?extid=97aae04ce27e39cbfca9
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1756c50e400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+97aae04ce27e39cbfca9@syzkaller.appspotmail.com

8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
8021q: adding VLAN 0 to HW filter on device team0
rcu: INFO: rcu_sched self-detected stall on CPU
rcu: 	0-....: (105000 ticks this GP) idle=2f6/1/0x4000000000000002  
softirq=23001/23001 fqs=26239
rcu: 	 (t=105008 jiffies g=49145 q=2382)
NMI backtrace for cpu 0
CPU: 0 PID: 8551 Comm: syz-executor7 Not tainted 4.18.0-next-20180824+ #47
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+0x1c9/0x2b4 lib/dump_stack.c:113
  nmi_cpu_backtrace.cold.3+0x48/0x88 lib/nmi_backtrace.c:101
  nmi_trigger_cpumask_backtrace+0x151/0x192 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:162 [inline]
  rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1340
  print_cpu_stall.cold.78+0x2fb/0x59c kernel/rcu/tree.c:1478
  check_cpu_stall kernel/rcu/tree.c:1550 [inline]
  __rcu_pending kernel/rcu/tree.c:3276 [inline]
  rcu_pending kernel/rcu/tree.c:3319 [inline]
  rcu_check_callbacks+0xd4a/0x15a0 kernel/rcu/tree.c:2665
  update_process_times+0x2d/0x70 kernel/time/timer.c:1636
  tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
  tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
  __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
  __hrtimer_run_queues+0x3eb/0xff0 kernel/time/hrtimer.c:1460
  hrtimer_interrupt+0x2f3/0x750 kernel/time/hrtimer.c:1518
  local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1029 [inline]
  smp_apic_timer_interrupt+0x16d/0x6a0 arch/x86/kernel/apic/apic.c:1054
  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:867
  </IRQ>
RIP: 0010:lock_release+0xa2/0x9f0 kernel/locking/lockdep.c:3910
Code: f2 c7 40 08 f2 f2 f2 f2 c7 40 0c 00 f2 f2 f2 c7 40 10 f2 f2 f2 f2 c7  
40 14 00 f2 f2 f2 65 48 8b 04 25 28 00 00 00 48 89 45 d0 <31> c0 48 89 f8  
48 c1 e8 03 0f b6 14 10 48 89 f8 83 e0 07 83 c0 03
RSP: 0018:ffff8801aa0078c8 EFLAGS: 00000292 ORIG_RAX: ffffffffffffff13
RAX: 2ec5cd2493d34200 RBX: 1ffff10035400f1e RCX: 0000000000000000
RDX: dffffc0000000000 RSI: 0000000000000000 RDI: ffff8801a9b56bbc
RBP: ffff8801aa0079f8 R08: 00000000000010df R09: 0000000000000001
R10: ffff8801a9b56be8 R11: 737c3e5c87308161 R12: ffff8801aa0079d0
R13: ffff8801c778d4c8 R14: ffff8801aa007ae0 R15: ffff8801a9b56380
  __might_fault+0x19e/0x1e0 mm/memory.c:4585
  _copy_from_user+0x30/0x150 lib/usercopy.c:10
  copy_from_user include/linux/uaccess.h:147 [inline]
  snd_seq_write+0x472/0x8d0 sound/core/seq/seq_clientmgr.c:1033
  __vfs_write+0x117/0x9d0 fs/read_write.c:485
  vfs_write+0x1fc/0x560 fs/read_write.c:549
  ksys_write+0x101/0x260 fs/read_write.c:598
  __do_sys_write fs/read_write.c:610 [inline]
  __se_sys_write fs/read_write.c:607 [inline]
  __x64_sys_write+0x73/0xb0 fs/read_write.c:607
  do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457089
Code: fd b4 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f09af65dc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f09af65e6d4 RCX: 0000000000457089
RDX: 00000000ffffff76 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d78a8 R14: 00000000004ca886 R15: 0000000000000000


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