general protection fault in d_alloc_pseudo

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ac5b84a1 Add linux-next specific files for 20190408
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=155bbd9b200000
kernel config:  https://syzkaller.appspot.com/x/.config?x=42a33a21877c9c95
dashboard link: https://syzkaller.appspot.com/bug?extid=57dc50baaee299931092
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=121029c3200000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13aa44fd200000

The bug was bisected to:

commit 56deac897903018e2672de8b784749f948e44be1
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Sat Mar 16 02:23:19 2019 +0000

    dcache: sort the freeing-without-RCU-delay mess for good.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1550bda7200000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=1750bda7200000
console output: https://syzkaller.appspot.com/x/log.txt?x=1350bda7200000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+57dc50baaee299931092@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 56deac897903 ("dcache: sort the freeing-without-RCU-delay mess for  
good.")

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7543 Comm: syz-executor982 Not tainted 5.1.0-rc3-next-20190408  
#20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:d_alloc_pseudo+0x33/0x70 fs/dcache.c:1752
Code: 41 54 49 89 fc 48 83 ec 08 e8 39 d9 b7 ff 4c 89 ee 4c 89 e7 e8 1e f1  
ff ff 48 ba 00 00 00 00 00 fc ff df 48 89 c1 48 c1 e9 03 <0f> b6 14 11 84  
d2 74 05 80 fa 03 7e 10 81 08 00 00 00 40 48 83 c4
RSP: 0018:ffff88808e77fd28 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 1ffff11011ceffad RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff81b8a01f RDI: 0000000000000282
RBP: ffff88808e77fd40 R08: ffff8880913c2380 R09: ffffed1015d25bc8
R10: ffffed1015d25bc7 R11: ffff8880ae92de3b R12: ffff88821b742cc0
R13: ffff88808e77fd88 R14: ffff88821b6a0628 R15: ffff888095d1f0f0
FS:  000000000195e880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004b6058 CR3: 000000008dafa000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 alloc_file_pseudo+0xe2/0x280 fs/file_table.c:224
 sock_alloc_file+0x4d/0x170 net/socket.c:406
 sock_map_fd net/socket.c:429 [inline]
 __sys_socket+0x150/0x220 net/socket.c:1495
 __do_sys_socket net/socket.c:1500 [inline]
 __se_sys_socket net/socket.c:1498 [inline]
 __x64_sys_socket+0x73/0xb0 net/socket.c:1498
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4412e9
Code: e8 ac e8 ff ff 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 0b 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdb62abef8 EFLAGS: 00000246 ORIG_RAX: 0000000000000029
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004412e9
RDX: 0000000000000073 RSI: 0000000000000002 RDI: 0000000000000002
RBP: 00000000006cc018 R08: 0000000000000001 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402180
R13: 0000000000402210 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 8205b4b5db42318a ]---
RIP: 0010:d_alloc_pseudo+0x33/0x70 fs/dcache.c:1752
Code: 41 54 49 89 fc 48 83 ec 08 e8 39 d9 b7 ff 4c 89 ee 4c 89 e7 e8 1e f1  
ff ff 48 ba 00 00 00 00 00 fc ff df 48 89 c1 48 c1 e9 03 <0f> b6 14 11 84  
d2 74 05 80 fa 03 7e 10 81 08 00 00 00 40 48 83 c4
RSP: 0018:ffff88808e77fd28 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 1ffff11011ceffad RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff81b8a01f RDI: 0000000000000282
RBP: ffff88808e77fd40 R08: ffff8880913c2380 R09: ffffed1015d25bc8
R10: ffffed1015d25bc7 R11: ffff8880ae92de3b R12: ffff88821b742cc0
R13: ffff88808e77fd88 R14: ffff88821b6a0628 R15: ffff888095d1f0f0
FS:  000000000195e880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004b6058 CR3: 000000008dafa000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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