Date:   Mon, 12 Mar 2018 07:02:01 -0700
From:   syzbot <syzbot+c5a3099b94cbdd9cd6da@...kaller.appspotmail.com>
To:     davem@...emloft.net, kuznet@....inr.ac.ru,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, yoshfuji@...ux-ipv6.org
Subject: WARNING in tcp_enter_loss (2)

Hello,

syzbot hit the following crash on net-next commit
a366e300ae9fc466d333e6d8f2bc5d58ed248041 (Wed Mar 7 16:43:19 2018 +0000)
ip6mr: remove synchronize_rcu() in favor of SOCK_RCU_FREE

Unfortunately, I don't have any reproducer for this crash yet.
Raw console output is attached.
compiler: gcc (GCC) 7.1.1 20170620
.config is attached.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c5a3099b94cbdd9cd6da@...kaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for  
details.
If you forward the report, please keep this part and the footer.

RAX: ffffffffffffffda RBX: 00007f2aae9136d4 RCX: 0000000000453e69
RDX: 0000000000000000 RSI: 0000000020000a80 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000015
R13: 0000000000000483 R14: 00000000006f6ce8 R15: 0000000000000000
WARNING: CPU: 0 PID: 4083 at net/ipv4/tcp_input.c:1955  
tcp_enter_loss+0xd28/0xff0 net/ipv4/tcp_input.c:1955
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 4083 Comm: rsyslogd Not tainted 4.16.0-rc4+ #256
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  <IRQ>
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x24d lib/dump_stack.c:53
  panic+0x1e4/0x41c kernel/panic.c:183
  __warn+0x1dc/0x200 kernel/panic.c:547
  report_bug+0x211/0x2d0 lib/bug.c:184
  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
  fixup_bug arch/x86/kernel/traps.c:247 [inline]
  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
  invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:986
RIP: 0010:tcp_enter_loss+0xd28/0xff0 net/ipv4/tcp_input.c:1955
RSP: 0000:ffff8801db207360 EFLAGS: 00010206
RAX: ffff8801b6cb2680 RBX: 0000000000000004 RCX: ffffffff84c7abe8
RDX: 0000000000000100 RSI: 0000000000000001 RDI: ffff8801d8352824
RBP: ffff8801db2073e0 R08: ffff88021fff801c R09: ffff88021fff8008
R10: 00000000fc3e77b6 R11: ffff88021fff801d R12: 0000000000000009
R13: ffff8801ab90ecb0 R14: dffffc0000000000 R15: ffff8801d8352000
  tcp_retransmit_timer+0xee0/0x2dd0 net/ipv4/tcp_timer.c:485
  tcp_write_timer_handler+0x335/0x820 net/ipv4/tcp_timer.c:572
  tcp_write_timer+0x153/0x170 net/ipv4/tcp_timer.c:592
  call_timer_fn+0x228/0x820 kernel/time/timer.c:1326
  expire_timers kernel/time/timer.c:1363 [inline]
  __run_timers+0x7ee/0xb70 kernel/time/timer.c:1666
  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
  __do_softirq+0x2d7/0xb85 kernel/softirq.c:285
  invoke_softirq kernel/softirq.c:365 [inline]
  irq_exit+0x1cc/0x200 kernel/softirq.c:405
  exiting_irq arch/x86/include/asm/apic.h:541 [inline]
  smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:857
  </IRQ>
RIP: 0033:0x41ca14
RSP: 002b:00007efd33621d60 EFLAGS: 00000207 ORIG_RAX: ffffffffffffff12
RAX: 0000000000000009 RBX: 0000000001f532e0 RCX: 656c6c616b7a7973
RDX: 0000000001f5346d RSI: 0000000001f1d1d9 RDI: 0000000001f53476
RBP: 0000000000000009 R08: 0000000001f1d1d0 R09: 00007efd35a00250
R10: 645f6b636f6c203f R11: 00007efd35a32a50 R12: 0000000001f1d1d0
R13: 0000000000000009 R14: 00000000000006c7 R15: 00007efd34e56da7
Dumping ftrace buffer:
    (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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