BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
PGD 800000018d85d067 P4D 800000018d85d067 PUD 175233067 PMD 0 
Oops: 0000 [#1] SMP PTI
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 14857 Comm: syz-executor4 Not tainted 4.17.0+ #4
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:__delayacct_blkio_end+0x5f/0x350 kernel/delayacct.c:82
RSP: 0018:ffff88017dedf068 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8801b1644318 RCX: 0000000000000000
RDX: ffff8801c5f5c318 RSI: aaaaaaaaaaaab000 RDI: ffffea0000000000
RBP: ffff88017dedf0f0 R08: 0000000000000000 R09: 0000000000000002
R10: 0000000000000000 R11: ffffffff819312c0 R12: ffff88013ae3a618
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000004
FS:  00007fb886db4700(0000) GS:ffff88021fc00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000004 CR3: 00000001c0ab0000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 delayacct_blkio_end include/linux/delayacct.h:128 [inline]
 try_to_wake_up+0xadb/0x2260 kernel/sched/core.c:2056
 default_wake_function+0x92/0xb0 kernel/sched/core.c:3762
 autoremove_wake_function+0x54/0x320 kernel/sched/wait.c:373
 wake_page_function+0x30b/0x320 mm/filemap.c:1010
 __wake_up_common+0x45a/0xa50 kernel/sched/wait.c:90
 __wake_up_locked_key_bookmark+0x74/0x80 kernel/sched/wait.c:165
 wake_up_page_bit+0x1e8/0x4d0 mm/filemap.c:1030
 unlock_page+0x110/0x160 mm/filemap.c:1207
 do_huge_pmd_wp_page+0xe32/0x50a0 mm/huge_memory.c:1289
 wp_huge_pmd mm/memory.c:3864 [inline]
 __handle_mm_fault mm/memory.c:4077 [inline]
 handle_mm_fault+0x232c/0x7ec0 mm/memory.c:4124
 __do_page_fault+0xec6/0x1a10 arch/x86/mm/fault.c:1400
 do_page_fault+0xb7/0x250 arch/x86/mm/fault.c:1477
 page_fault+0x1e/0x30 arch/x86/entry/entry_64.S:1160
RIP: 0010:copy_user_generic_unrolled+0x89/0xc0 arch/x86/lib/copy_user_64.S:66
RSP: 0018:ffff88017dedfa90 EFLAGS: 00010202
RAX: ffffffff83ffa7db RBX: 0000000020000400 RCX: 0000000000000004
RDX: 0000000000000000 RSI: ffff88017dedfb30 RDI: 0000000020000400
RBP: ffff88017dedfaf8 R08: 0000000000000013 R09: 00000000d0600072
R10: 0000000000000001 R11: ffff88013e68c350 R12: 0000000000000000
R13: ffff88017dedfa98 R14: 0000000000000000 R15: ffff88013ae3a618
 copy_to_user include/linux/uaccess.h:183 [inline]
 userfaultfd_read+0x1e29/0x2940 fs/userfaultfd.c:1184
 __vfs_read+0x1b2/0x9d0 fs/read_write.c:416
 vfs_read+0x36c/0x6b0 fs/read_write.c:452
 ksys_read fs/read_write.c:578 [inline]
 __do_sys_read fs/read_write.c:588 [inline]
 __se_sys_read fs/read_write.c:586 [inline]
 __x64_sys_read+0x1bf/0x3e0 fs/read_write.c:586
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4559f9
RSP: 002b:00007fb886db3c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fb886db46d4 RCX: 00000000004559f9
RDX: 0000000000000064 RSI: 0000000020000400 RDI: 0000000000000013
RBP: 000000000072bf50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004bfbb0 R14: 00000000004cfa60 R15: 0000000000000001
Code: ff 0f 85 72 02 00 00 4c 8b 33 48 89 df e8 fa 2f 58 00 48 8b 00 8b 0a 89 4d d0 4d 8d 7e 04 48 89 45 b0 48 85 c0 0f 85 5b 02 00 00 <41> 8b 5e 04 4c 89 ff e8 95 2f 58 00 8b 30 83 e6 01 89 f0 f7 d0 
RIP: __delayacct_blkio_end+0x5f/0x350 kernel/delayacct.c:82 RSP: ffff88017dedf068
CR2: 0000000000000004
---[ end trace 9507280ded076141 ]---