BUG: unable to handle kernel NULL pointer dereference at           (null)
IP: proc_flush_task_mnt fs/proc/base.c:3056 [inline]
IP: proc_flush_task+0x8a/0x1c0 fs/proc/base.c:3128
PGD 214dd0067 P4D 214dd0067 PUD 2137d6067 PMD 0 
Oops: 0000 [#1] SMP
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 3142 Comm: syz-executor3 Not tainted 4.15.0-rc3-next-20171214+ #67
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:proc_flush_task_mnt fs/proc/base.c:3056 [inline]
RIP: 0010:proc_flush_task+0x8a/0x1c0 fs/proc/base.c:3128
RSP: 0018:ffffc9000189bc30 EFLAGS: 00010282
RAX: 0000000000000001 RBX: 0000000000000002 RCX: ffffffff825bf264
RDX: 0000000000000000 RSI: ffffc9000189bc58 RDI: ffffc9000189bc4d
RBP: ffffc9000189bc90 R08: 0000000000000000 R09: 0000000000000002
R10: ffffc9000189bad8 R11: 0000000000000002 R12: ffffc9000189bc4d
R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000004
FS:  0000000001470940(0000) GS:ffff88021fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000213771003 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 release_task+0xf4/0x750 kernel/exit.c:195
 wait_task_zombie kernel/exit.c:1165 [inline]
 wait_consider_task+0xe83/0xfb0 kernel/exit.c:1392
 do_wait_thread kernel/exit.c:1455 [inline]
 do_wait+0x189/0x3d0 kernel/exit.c:1526
 kernel_wait4+0xac/0x170 kernel/exit.c:1669
 SYSC_wait4+0xb0/0xc0 kernel/exit.c:1681
 SyS_wait4+0x2c/0x40 kernel/exit.c:1677
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x40cdba
RSP: 002b:00007fff9cfdb6b8 EFLAGS: 00000246 ORIG_RAX: 000000000000003d
RAX: ffffffffffffffda RBX: 0000000001470914 RCX: 000000000040cdba
RDX: 0000000040000001 RSI: 00007fff9cfdb6dc RDI: ffffffffffffffff
RBP: 00000000000024a9 R08: 0000000000000001 R09: 0000000001470940
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000000024a9
R13: 000000000000001f R14: 000000000002eceb R15: 0000000000000001
Code: d0 48 c1 e2 04 44 8b 3c 11 48 c7 c2 ec d7 f5 82 44 8b 68 30 48 8b 40 38 4c 8b 70 58 44 89 e9 e8 dd 83 10 01 89 45 cc 48 8d 75 c8 <49> 8b 3e e8 6e 9d f7 ff 48 85 c0 48 89 45 a8 74 1d e8 60 2d e0 
RIP: proc_flush_task_mnt fs/proc/base.c:3056 [inline] RSP: ffffc9000189bc30
RIP: proc_flush_task+0x8a/0x1c0 fs/proc/base.c:3128 RSP: ffffc9000189bc30
CR2: 0000000000000000
---[ end trace 96968f6879f5e625 ]---