Re: WARNING in port_delete

[syzbot <syzbot+e4c8abb920efa77bace9@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following crash on:

HEAD commit:    091a1eaa0e30 Merge branch 'akpm'
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16623e59400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c0af03fe452b65fb
dashboard link: https://syzkaller.appspot.com/bug?extid=e4c8abb920efa77bace9
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=102e2c91400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+e4c8abb920efa77bace9@syzkaller.appspotmail.com

WARNING: CPU: 1 PID: 23693 at sound/core/seq/seq_ports.c:275  
port_delete+0x177/0x1b0 sound/core/seq/seq_ports.c:275
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 23693 Comm: syz-executor0 Not tainted 4.19.0-rc6+ #47
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:77 [inline]
  dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
  panic+0x238/0x4e7 kernel/panic.c:184
  __warn.cold.8+0x163/0x1ba kernel/panic.c:536
  report_bug+0x254/0x2d0 lib/bug.c:186
  fixup_bug arch/x86/kernel/traps.c:178 [inline]
  do_error_trap+0x1fc/0x4d0 arch/x86/kernel/traps.c:296
kobject: 'loop1' (00000000baf940ef): kobject_uevent_env
kobject: 'loop1' (00000000baf940ef): fill_kobj_path: path  
= '/devices/virtual/block/loop1'
  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:993
RIP: 0010:port_delete+0x177/0x1b0 sound/core/seq/seq_ports.c:275
Code: e7 99 fb 45 85 e4 75 14 e8 66 e6 99 fb 48 89 df e8 ee 29 dd fb 31 c0  
5b 41 5c 5d c3 e8 52 e6 99 fb 0f 0b eb e3 e8 49 e6 99 fb <0f> 0b eb 9b e8  
a0 55 dd fb eb bd e8 99 55 dd fb e9 77 ff ff ff e8
RSP: 0018:ffff8801a7477890 EFLAGS: 00010293
RAX: ffff8801a84e05c0 RBX: ffff8801cf0be4c0 RCX: ffffffff85e4eee1
RDX: 0000000000000000 RSI: ffffffff85e4ef47 RDI: 0000000000000005
RBP: ffff8801a74778a0 R08: ffff8801a84e05c0 R09: 00000000deede79a
R10: 00000000da8ba726 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8801cf0be510 R14: 1ffff10034e8ef20 R15: ffff8801cb447b00
  snd_seq_delete_port+0x3cb/0x4a0 sound/core/seq/seq_ports.c:303
  snd_seq_ioctl_delete_port+0xba/0x190 sound/core/seq/seq_clientmgr.c:1324
  snd_seq_kernel_client_ctl+0x15a/0x190 sound/core/seq/seq_clientmgr.c:2353
  snd_seq_event_port_detach+0xfc/0x170 sound/core/seq/seq_ports.c:705
  delete_port+0x7d/0xc0 sound/core/seq/oss/seq_oss_init.c:354
  snd_seq_oss_release+0xf2/0x130 sound/core/seq/oss/seq_oss_init.c:433
  odev_release+0x52/0x70 sound/core/seq/oss/seq_oss.c:153
  __fput+0x385/0xa30 fs/file_table.c:278
  ____fput+0x15/0x20 fs/file_table.c:309
  task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
  tracehook_notify_resume include/linux/tracehook.h:193 [inline]
  exit_to_usermode_loop+0x318/0x380 arch/x86/entry/common.c:166
  prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
  do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457579
Code: 1d 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 eb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f85fa204c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000457579
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000006
RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f85fa2056d4
R13: 00000000004ef912 R14: 00000000004cc460 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..