BUG: corrupted list in locks_delete_block

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    442b8cea2477 Add linux-next specific files for 20181109
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12b1262b400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2f72bdb11df9fbe8
dashboard link: https://syzkaller.appspot.com/bug?extid=13eb7470890c56ce3f37
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=107566a3400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11b5fa2b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+13eb7470890c56ce3f37@xxxxxxxxxxxxxxxxxxxxxxxxx

list_del corruption. prev->next should be ffff8801c135f960, but was  
0000000000000007
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:53!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5972 Comm: syz-executor001 Not tainted  
4.20.0-rc1-next-20181109+ #110
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__list_del_entry_valid.cold.1+0x48/0x4a lib/list_debug.c:51
Code: fe 60 88 e8 72 9b d3 fd 0f 0b 48 89 de 48 c7 c7 40 00 61 88 e8 61 9b  
d3 fd 0f 0b 48 89 de 48 c7 c7 e0 ff 60 88 e8 50 9b d3 fd <0f> 0b 48 89 d9  
48 c7 c7 a0 00 61 88 e8 3f 9b d3 fd 0f 0b 48 89 f1
RSP: 0018:ffff8801c135f750 EFLAGS: 00010286
RAX: 0000000000000054 RBX: ffff8801c135f960 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8165ba15 RDI: 0000000000000005
RBP: ffff8801c135f768 R08: ffff8801c11ce080 R09: ffffed003b5e5020
R10: ffffed003b5e5020 R11: ffff8801daf28107 R12: ffff8801d945f3a0
R13: ffff8801d945f3a0 R14: 0000000000000000 R15: ffff8801c135f838
FS:  00007f96b449c700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000046aa40 CR3: 00000001b39ab000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 __list_del_entry include/linux/list.h:117 [inline]
 list_del_init include/linux/list.h:159 [inline]
 __locks_delete_block fs/locks.c:683 [inline]
 locks_delete_block+0xce/0x3d0 fs/locks.c:716
 locks_mandatory_area+0x48b/0x6a0 fs/locks.c:1398
 rw_verify_area+0x2f2/0x360 fs/read_write.c:386
 do_iter_write+0x101/0x5f0 fs/read_write.c:954
 vfs_writev+0x1f1/0x360 fs/read_write.c:1004
 do_writev+0x11a/0x310 fs/read_write.c:1039
 __do_sys_writev fs/read_write.c:1112 [inline]
 __se_sys_writev fs/read_write.c:1109 [inline]
 __x64_sys_writev+0x75/0xb0 fs/read_write.c:1109
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x446619
Code: e8 6c b4 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 2b 09 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f96b449bda8 EFLAGS: 00000297 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00000000006dbc38 RCX: 0000000000446619
RDX: 0000000000000001 RSI: 0000000020000440 RDI: 0000000000000003
RBP: 00000000006dbc30 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 00000000006dbc3c
R13: 2f30656c69662f2e R14: 64663d736e617274 R15: 00000000006dbd2c
Modules linked in:
---[ end trace efdc3057b60b19f3 ]---
RIP: 0010:__list_del_entry_valid.cold.1+0x48/0x4a lib/list_debug.c:51
Code: fe 60 88 e8 72 9b d3 fd 0f 0b 48 89 de 48 c7 c7 40 00 61 88 e8 61 9b  
d3 fd 0f 0b 48 89 de 48 c7 c7 e0 ff 60 88 e8 50 9b d3 fd <0f> 0b 48 89 d9  
48 c7 c7 a0 00 61 88 e8 3f 9b d3 fd 0f 0b 48 89 f1
RSP: 0018:ffff8801c135f750 EFLAGS: 00010286
RAX: 0000000000000054 RBX: ffff8801c135f960 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8165ba15 RDI: 0000000000000005
RBP: ffff8801c135f768 R08: ffff8801c11ce080 R09: ffffed003b5e5020
R10: ffffed003b5e5020 R11: ffff8801daf28107 R12: ffff8801d945f3a0
R13: ffff8801d945f3a0 R14: 0000000000000000 R15: ffff8801c135f838
FS:  00007f96b449c700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000046aa40 CR3: 00000001b39ab000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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