WARNING in rds_message_alloc_sgs

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    6201f31a39f8 Add linux-next specific files for 20181030
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1397d06d400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2a22859d870756c1
dashboard link: https://syzkaller.appspot.com/bug?extid=26de17458aeda9d305d8
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10bb52eb400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=118bdfc5400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+26de17458aeda9d305d8@xxxxxxxxxxxxxxxxxxxxxxxxx

WARNING: CPU: 0 PID: 19789 at net/rds/message.c:316  
rds_message_alloc_sgs+0x10c/0x160 net/rds/message.c:316
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 19789 Comm: syz-executor827 Not tainted 4.19.0-next-20181030+  
#101
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 panic+0x2ad/0x55c kernel/panic.c:188
 __warn.cold.8+0x20/0x45 kernel/panic.c:540
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:rds_message_alloc_sgs+0x10c/0x160 net/rds/message.c:316
Code: c0 74 04 3c 03 7e 6c 44 01 ab 78 01 00 00 e8 2b 9e 35 fa 4c 89 e0 48  
83 c4 08 5b 41 5c 41 5d 41 5e 41 5f 5d c3 e8 14 9e 35 fa <0f> 0b 31 ff 44  
89 ee e8 18 9f 35 fa 45 85 ed 75 1b e8 fe 9d 35 fa
RSP: 0018:ffff8801c51b7460 EFLAGS: 00010293
RAX: ffff8801bc412080 RBX: ffff8801d7bf4040 RCX: ffffffff8749c9e6
RDX: 0000000000000000 RSI: ffffffff8749ca5c RDI: 0000000000000004
RBP: ffff8801c51b7490 R08: ffff8801bc412080 R09: ffffed003b5c5b67
R10: ffffed003b5c5b67 R11: ffff8801dae2db3b R12: 0000000000000000
R13: 000000000007165c R14: 000000000007165c R15: 0000000000000005
 rds_cmsg_rdma_args+0x82d/0x1510 net/rds/rdma.c:623
 rds_cmsg_send net/rds/send.c:971 [inline]
 rds_sendmsg+0x19a2/0x3180 net/rds/send.c:1273
 sock_sendmsg_nosec net/socket.c:622 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:632
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2117
 __sys_sendmsg+0x11d/0x280 net/socket.c:2155
 __do_sys_sendmsg net/socket.c:2164 [inline]
 __se_sys_sendmsg net/socket.c:2162 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2162
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x44a859
Code: e8 dc e6 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 6b cb fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f1d4710ada8 EFLAGS: 00000297 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dcc28 RCX: 000000000044a859
RDX: 0000000000000000 RSI: 0000000020001600 RDI: 0000000000000003
RBP: 00000000006dcc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000297 R12: 00000000006dcc2c
R13: 646e732f7665642f R14: 00007f1d4710b9c0 R15: 00000000006dcd2c
Kernel Offset: disabled
Rebooting in 86400 seconds..


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