INFO: rcu detected stall in netlink_sendmsg

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ce28bb445388 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=12662e67400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=67a2081147a23142
dashboard link: https://syzkaller.appspot.com/bug?extid=a910a514846e27f15348
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+a910a514846e27f15348@xxxxxxxxxxxxxxxxxxxxxxxxx

netlink: 8 bytes leftover after parsing attributes in process  
`syz-executor5'.
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (10500 ticks this GP) idle=58a/1/0x4000000000000002  
softirq=84145/84145 fqs=0
rcu: 	 (t=10500 jiffies g=122913 q=1655)
rcu: rcu_preempt kthread starved for 10500 jiffies! g122913 f0x0  
RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=1
rcu: RCU grace-period kthread stack dump:
rcu_preempt     I22568    10      2 0x80000000
Call Trace:
 context_switch kernel/sched/core.c:2831 [inline]
 __schedule+0x86c/0x1ed0 kernel/sched/core.c:3472
 schedule+0xfe/0x460 kernel/sched/core.c:3516
 schedule_timeout+0x140/0x260 kernel/time/timer.c:1804
 rcu_gp_fqs_loop+0x762/0xa80 kernel/rcu/tree.c:1934
 rcu_gp_kthread+0x341/0xc70 kernel/rcu/tree.c:2090
 kthread+0x35a/0x440 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
NMI backtrace for cpu 1
CPU: 1 PID: 10942 Comm: syz-executor1 Not tainted 4.20.0-rc7+ #358
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+0x1d3/0x2c6 lib/dump_stack.c:113
 nmi_cpu_backtrace.cold.4+0x63/0xa2 lib/nmi_backtrace.c:101
 nmi_trigger_cpumask_backtrace+0x1c2/0x22c 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:164 [inline]
 rcu_dump_cpu_stacks+0x16f/0x1bc kernel/rcu/tree.c:1195
 print_cpu_stall.cold.65+0x1f3/0x3c6 kernel/rcu/tree.c:1334
 check_cpu_stall kernel/rcu/tree.c:1408 [inline]
 rcu_pending kernel/rcu/tree.c:2961 [inline]
 rcu_check_callbacks+0xac1/0x1410 kernel/rcu/tree.c:2506
 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:1034 [inline]
 smp_apic_timer_interrupt+0x1a1/0x760 arch/x86/kernel/apic/apic.c:1059
 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:807
 </IRQ>
RIP: 0010:__sanitizer_cov_trace_const_cmp4+0x1/0x20 kernel/kcov.c:188
Code: fe ff ff 5d c3 0f 1f 40 00 55 0f b7 d6 0f b7 f7 bf 03 00 00 00 48 89  
e5 48 8b 4d 08 e8 88 fe ff ff 5d c3 66 0f 1f 44 00 00 55 <89> f2 89 fe bf  
05 00 00 00 48 89 e5 48 8b 4d 08 e8 6a fe ff ff 5d
RSP: 0018:ffff8881c195ef50 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff13
RAX: 0000000000040000 RBX: 0000000000000004 RCX: ffffc90005f36000
RDX: 0000000000040000 RSI: 0000000000000004 RDI: 000000000000000e
RBP: ffff8881c195efc0 R08: ffff8881d7da2040 R09: 0000000000000000
R10: 0000000000000000 R11: ffff8881d7da2040 R12: dffffc0000000000
R13: ffff8881c2e07c18 R14: ffff8881b8142d20 R15: 0000000001000000
 xfrm_policy_bysel_ctx+0x883/0x1050 net/xfrm/xfrm_policy.c:1664
 xfrm_get_policy+0x6a3/0x1140 net/xfrm/xfrm_user.c:1887
 xfrm_user_rcv_msg+0x44c/0x8e0 net/xfrm/xfrm_user.c:2663
 netlink_rcv_skb+0x16c/0x430 net/netlink/af_netlink.c:2477
 xfrm_netlink_rcv+0x6f/0x90 net/xfrm/xfrm_user.c:2671
 netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
 netlink_unicast+0x59f/0x750 net/netlink/af_netlink.c:1336
 netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457669
Code: fd b3 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 b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc47e41ac78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457669
RDX: 0000000000000000 RSI: 000000002014f000 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fc47e41b6d4
R13: 00000000004c44d8 R14: 00000000004d74e8 R15: 00000000ffffffff


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