BUG: unable to handle kernel NULL pointer dereference at 0000000000000020
IP: __read_once_size include/linux/compiler.h:183 [inline]
IP: compound_head include/linux/page-flags.h:147 [inline]
IP: page_mapping+0x13/0x130 mm/util.c:475
PGD 1fb713067 P4D 1fb713067 PUD 1f868b067 PMD 0 
Oops: 0000 [#1] SMP
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 5974 Comm: syz-executor1 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:__read_once_size include/linux/compiler.h:183 [inline]
RIP: 0010:compound_head include/linux/page-flags.h:147 [inline]
RIP: 0010:page_mapping+0x13/0x130 mm/util.c:475
RSP: 0018:ffffc90000effae8 EFLAGS: 00010216
RAX: 0000000000010000 RBX: 0000000000000000 RCX: ffffffff81378423
RDX: 00000000000001f4 RSI: ffffc90005ef8000 RDI: 0000000000000000
RBP: ffffc90000effb08 R08: 0000000000000000 R09: ffff8801f85c9e30
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801f85c9d80
R13: ffff8801f85c9c00 R14: ffff8801fe59b2c0 R15: ffff88020d697600
FS:  00007f09935d4700(0000) GS:ffff88021fd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000020 CR3: 00000001f9fe3001 CR4: 00000000001606e0
Call Trace:
 set_page_dirty+0x1b/0x150 mm/page-writeback.c:2544
 rds_atomic_free_op+0x25/0x80 net/rds/rdma.c:481
 rds_message_purge net/rds/message.c:79 [inline]
 rds_message_put+0x174/0x1b0 net/rds/message.c:91
 rds_sendmsg+0x7ac/0xcb0 net/rds/send.c:1204
 sock_sendmsg_nosec net/socket.c:636 [inline]
 sock_sendmsg+0x51/0x70 net/socket.c:646
 ___sys_sendmsg+0x155/0x3b0 net/socket.c:2026
 __sys_sendmmsg+0xd1/0x290 net/socket.c:2116
 SYSC_sendmmsg net/socket.c:2147 [inline]
 SyS_sendmmsg+0x35/0x60 net/socket.c:2142
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452a09
RSP: 002b:00007f09935d3c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452a09
RDX: 0000000000000001 RSI: 0000000020573000 RDI: 0000000000000013
RBP: 0000000000000020 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006ed3a0
R13: 00000000ffffffff R14: 00007f09935d46d4 R15: 0000000000000000
Code: 44 1f f4 ff 48 c7 c7 c8 58 a4 82 e8 b6 20 24 01 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 56 41 55 41 54 53 48 89 fb e8 1d 1f f4 ff <4c> 8b 63 20 41 f6 c4 01 0f 85 c8 00 00 00 e8 0a 1f f4 ff 4c 8b 
RIP: __read_once_size include/linux/compiler.h:183 [inline] RSP: ffffc90000effae8
RIP: compound_head include/linux/page-flags.h:147 [inline] RSP: ffffc90000effae8
RIP: page_mapping+0x13/0x130 mm/util.c:475 RSP: ffffc90000effae8
CR2: 0000000000000020
---[ end trace 0b53726cca471bd6 ]---