=============================
WARNING: suspicious RCU usage
4.15.0+ #219 Not tainted
-----------------------------
./include/linux/inetdevice.h:216 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by syzkaller165559/4088:
 #0:  (&tfile->napi_mutex){+.+.}, at: [<0000000053751807>] tun_get_user+0xe6c/0x3940 drivers/net/tun.c:1817
 #1:  ((&im->timer)){+.-.}, at: [<00000000aafe5b62>] lockdep_copy_map include/linux/lockdep.h:178 [inline]
 #1:  ((&im->timer)){+.-.}, at: [<00000000aafe5b62>] call_timer_fn+0x1c6/0x820 kernel/time/timer.c:1316
 #2:  (&(&im->lock)->rlock){+.-.}, at: [<00000000d89a4377>] spin_lock_bh include/linux/spinlock.h:315 [inline]
 #2:  (&(&im->lock)->rlock){+.-.}, at: [<00000000d89a4377>] igmpv3_send_report+0x98/0x5b0 net/ipv4/igmp.c:600

stack backtrace:
CPU: 1 PID: 4088 Comm: syzkaller165559 Not tainted 4.15.0+ #219
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+0x194/0x257 lib/dump_stack.c:53
 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4592
 __in_dev_get_rcu include/linux/inetdevice.h:216 [inline]
 igmpv3_get_srcaddr net/ipv4/igmp.c:329 [inline]
 igmpv3_newpack+0xeef/0x12e0 net/ipv4/igmp.c:389
 add_grhead.isra.27+0x235/0x300 net/ipv4/igmp.c:432
 add_grec+0xbd3/0x1170 net/ipv4/igmp.c:565
 igmpv3_send_report+0xd5/0x5b0 net/ipv4/igmp.c:605
 igmp_send_report+0xc43/0x1050 net/ipv4/igmp.c:722
 igmp_timer_expire+0x322/0x5c0 net/ipv4/igmp.c:831
 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
 do_softirq_own_stack+0x2a/0x40 arch/x86/entry/entry_64.S:1151
 </IRQ>
 do_softirq.part.19+0x14d/0x190 kernel/softirq.c:329
 do_softirq kernel/softirq.c:177 [inline]
 __local_bh_enable_ip+0x1ee/0x230 kernel/softirq.c:182
 local_bh_enable include/linux/bottom_half.h:32 [inline]
 tun_get_user+0x2776/0x3940 drivers/net/tun.c:1942
 tun_chr_write_iter+0xb9/0x160 drivers/net/tun.c:1986
 call_write_iter include/linux/fs.h:1781 [inline]
 do_iter_readv_writev+0x55c/0x830 fs/read_write.c:653
 do_iter_write+0x154/0x540 fs/read_write.c:932
 vfs_writev+0x18a/0x340 fs/read_write.c:977
 do_writev+0xfc/0x2a0 fs/read_write.c:1012
 SYSC_writev fs/read_write.c:1085 [inline]
 SyS_writev+0x27/0x30 fs/read_write.c:1082
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x445370
RSP: 002b:00007ffc19e6aeb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000445370
RDX: 0000000000000001 RSI: 00007ffc19e6aec0 RDI: 0000000000000003
RBP: 0000000000000004 R08: 000000000000fd15 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 000000000000000c R14: 0000000000000000 R15: 0000000000000000