INFO: rcu detected stall in pppol2tp_sendmsg

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    11da3a7f84f1 Linux 4.19-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10577ada400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9917ff4b798e1a1e
dashboard link: https://syzkaller.appspot.com/bug?extid=0925ea3f5745e9005733
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0925ea3f5745e9005733@xxxxxxxxxxxxxxxxxxxxxxxxx

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (1 GPs behind) idle=142/1/0x4000000000000002  
softirq=27118/27119 fqs=5247
rcu: 	 (t=10500 jiffies g=38069 q=255)
NMI backtrace for cpu 0
CPU: 0 PID: 11502 Comm: syz-executor2 Not tainted 4.19.0-rc3+ #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 <IRQ>
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1c4/0x2b4 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.3+0x63/0xa2 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1b3/0x1ed lib/nmi_backtrace.c:62
 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 trigger_single_cpu_backtrace include/linux/nmi.h:162 [inline]
 rcu_dump_cpu_stacks+0x175/0x1c2 kernel/rcu/tree.c:1340
 print_cpu_stall.cold.78+0x2d3/0x524 kernel/rcu/tree.c:1478
 check_cpu_stall kernel/rcu/tree.c:1550 [inline]
 __rcu_pending kernel/rcu/tree.c:3276 [inline]
 rcu_pending kernel/rcu/tree.c:3319 [inline]
 rcu_check_callbacks+0xfd9/0x1990 kernel/rcu/tree.c:2665
 update_process_times+0x2d/0x70 kernel/time/timer.c:1636
 tick_sched_handle+0x9f/0x180 kernel/time/tick-sched.c:164
 tick_sched_timer+0x45/0x130 kernel/time/tick-sched.c:1274
 __run_hrtimer kernel/time/hrtimer.c:1398 [inline]
 __hrtimer_run_queues+0x41c/0x10d0 kernel/time/hrtimer.c:1460
 hrtimer_interrupt+0x313/0x780 kernel/time/hrtimer.c:1518
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1029 [inline]
 smp_apic_timer_interrupt+0x1a1/0x760 arch/x86/kernel/apic/apic.c:1054
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:864
 </IRQ>
RIP: 0010:security_xfrm_policy_lookup+0x58/0xd0 security/security.c:1675
Code: 3b fe 41 0f b6 c5 49 bc 00 00 00 00 00 fc ff df 89 45 d4 e8 1a f2 3b  
fe 48 8d 7b 18 48 89 f8 48 c1 e8 03 42 80 3c 20 00 75 58 <8b> 55 d4 44 89  
fe 4c 89 f7 48 8b 43 18 e8 36 91 9d 04 31 ff 41 89
RSP: 0018:ffff8801ba216ee0 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13
RAX: 1ffffffff1317fd6 RBX: ffffffff898bfe98 RCX: ffffc90005017000
RDX: 0000000000040000 RSI: ffffffff8342dea6 RDI: ffffffff898bfeb0
RBP: ffff8801ba216f10 R08: ffff8801d2b54480 R09: 1ffffffff12b43d5
R10: ffffed003b5c4732 R11: ffff8801dae23993 R12: dffffc0000000000
R13: 0000000000000001 R14: 0000000000000000 R15: 00000000000000df
 xfrm_sk_policy_lookup+0x32b/0x640 net/xfrm/xfrm_policy.c:1203
 xfrm_lookup_with_ifid+0x2a1/0x2b80 net/xfrm/xfrm_policy.c:2063
 xfrm_lookup net/xfrm/xfrm_policy.c:2200 [inline]
 xfrm_lookup_route+0x3c/0x1f0 net/xfrm/xfrm_policy.c:2211
 ip6_dst_lookup_flow+0x1c6/0x270 net/ipv6/ip6_output.c:1085
 inet6_csk_route_socket+0x8bd/0x1020 net/ipv6/inet6_connection_sock.c:110
 inet6_csk_xmit+0x118/0x630 net/ipv6/inet6_connection_sock.c:125
 l2tp_xmit_core net/l2tp/l2tp_core.c:1030 [inline]
 l2tp_xmit_skb+0x1465/0x1860 net/l2tp/l2tp_core.c:1132
 pppol2tp_sendmsg+0x4b1/0x6c0 net/l2tp/l2tp_ppp.c:329
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x51d/0x930 net/socket.c:2114
 __sys_sendmmsg+0x246/0x6d0 net/socket.c:2209
 __do_sys_sendmmsg net/socket.c:2238 [inline]
 __se_sys_sendmmsg net/socket.c:2235 [inline]
 __x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2235
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4572a9
Code: fd b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 cb b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7ab090fc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00007f7ab09106d4 RCX: 00000000004572a9
RDX: 0800000000000059 RSI: 0000000020005fc0 RDI: 0000000000000006
RBP: 00000000009300a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d4a20 R14: 00000000004c8fe5 R15: 0000000000000000


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