BUG: unable to handle kernel paging request in locks_remove_file

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    d881de30d29e Add linux-next specific files for 20181107
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1103882b400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=caa433e1c8778437
dashboard link: https://syzkaller.appspot.com/bug?extid=1d200d0b1db9c9f449d0
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+1d200d0b1db9c9f449d0@xxxxxxxxxxxxxxxxxxxxxxxxx

kernel tried to execute NX-protected page - exploit attempt? (uid: 0)
BUG: unable to handle kernel paging request at ffff880194657bb8
PGD be01067 P4D be01067 PUD 1bf029063 PMD 80000001946001e3
Oops: 0011 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8074 Comm: syz-executor4 Not tainted 4.20.0-rc1-next-20181107+  
#107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:0xffff880194657bb8
Code: c1 eb 86 af 8c 32 00 f1 ff 1f d0 7c 65 94 01 88 ff ff f8 7d 65 94 01  
88 ff ff 00 00 00 00 00 fc ff df 04 00 00 00 00 00 00 00 <78> 7d 65 94 01  
88 ff ff bc 9e 2b 81 ff ff ff ff 38 89 d3 8c 01 88
kobject: 'loop5' (00000000fd72d949): kobject_uevent_env
RSP: 0018:ffff880194657508 EFLAGS: 00010212
RAX: 0000000000040000 RBX: ffff880194657bb8 RCX: ffffc9000a5f1000
RDX: 000000000000039f RSI: ffffffff81ed5c9e RDI: ffff880194657588
RBP: ffff8801946576f0 R08: ffff88018cd380c0 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d9678080
R13: ffff880194657588 R14: 1ffff100328caea5 R15: dffffc0000000000
kobject: 'loop5' (00000000fd72d949): fill_kobj_path: path  
= '/devices/virtual/block/loop5'
FS:  00007f5f1e438700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff880194657bb8 CR3: 00000001cd753000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
kobject: 'loop3' (00000000367508b9): kobject_uevent_env
Call Trace:
kobject: 'loop3' (00000000367508b9): fill_kobj_path: path  
= '/devices/virtual/block/loop3'
 locks_remove_file+0x148/0x5c0 fs/locks.c:2607
 __fput+0x2f0/0xa70 fs/file_table.c:271
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 get_signal+0x1550/0x1970 kernel/signal.c:2347
 do_signal+0x9c/0x21c0 arch/x86/kernel/signal.c:816
 exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
 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: 0033:0x457569
Code: fd b3 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 b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5f1e437c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000049
RAX: fffffffffffffe00 RBX: 0000000000000002 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5f1e4386d4
R13: 00000000004bdd9e R14: 00000000004ccdb8 R15: 00000000ffffffff
Modules linked in:
CR2: ffff880194657bb8
---[ end trace f5c1663e01f0c934 ]---
RIP: 0010:0xffff880194657bb8
Code: c1 eb 86 af 8c 32 00 f1 ff 1f d0 7c 65 94 01 88 ff ff f8 7d 65 94 01  
88 ff ff 00 00 00 00 00 fc ff df 04 00 00 00 00 00 00 00 <78> 7d 65 94 01  
88 ff ff bc 9e 2b 81 ff ff ff ff 38 89 d3 8c 01 88
RSP: 0018:ffff880194657508 EFLAGS: 00010212
RAX: 0000000000040000 RBX: ffff880194657bb8 RCX: ffffc9000a5f1000
RDX: 000000000000039f RSI: ffffffff81ed5c9e RDI: ffff880194657588
RBP: ffff8801946576f0 R08: ffff88018cd380c0 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d9678080
R13: ffff880194657588 R14: 1ffff100328caea5 R15: dffffc0000000000
FS:  00007f5f1e438700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff880194657bb8 CR3: 00000001cd753000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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