===============================
[ INFO: suspicious RCU usage. ]
4.9.111-g03c70fe #58 Not tainted
-------------------------------
kernel/rcu/tree_plugin.h:678 Illegal synchronize_rcu() in RCU read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
2 locks held by loop0/17624:
 #0:  (rcu_read_lock){......}, at: [<ffffffff81cf7143>] avc_has_perm_noaudit+0xa3/0x450 security/selinux/avc.c:1108
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128784e>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 1 PID: 17624 Comm: loop0 Not tainted 4.9.111-g03c70fe #58
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb2729 ffff8801c0598000 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801b26b0658 ffff8801db307d90
 ffffffff81426090 ffff8801b26b0500 ffff8801cd1f9948 ffff8801cd1f9148
Call Trace:
 <IRQ> [  895.947646]  [<ffffffff81eb2729>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  895.947646]  [<ffffffff81eb2729>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81426090>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff812840e8>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836bbeda>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bc267>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bcb22>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff83020095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff8128776e>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff8128776e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff8128776e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff8128776e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff8128776e>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff839ff8bb>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b237>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b237>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839fe4a1>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839fe4a1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fa630>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> 
 [<ffffffff81cf7175>] rcu_lock_acquire include/linux/rcupdate.h:493 [inline]
 [<ffffffff81cf7175>] rcu_read_lock include/linux/rcupdate.h:875 [inline]
 [<ffffffff81cf7175>] avc_has_perm_noaudit+0xd5/0x450 security/selinux/avc.c:1110
 [<ffffffff81d05fca>] cred_has_capability+0x13a/0x2e0 security/selinux/hooks.c:1666
 [<ffffffff81d061be>] selinux_vm_enough_memory+0x4e/0x60 security/selinux/hooks.c:2255
 [<ffffffff81cec4d7>] security_vm_enough_memory_mm+0x77/0xb0 security/security.c:232
 [<ffffffff8148a2ab>] shmem_acct_block mm/shmem.c:174 [inline]
 [<ffffffff8148a2ab>] shmem_alloc_and_acct_page+0x47b/0x790 mm/shmem.c:1438
 [<ffffffff8148c262>] shmem_getpage_gfp+0x332/0x1de0 mm/shmem.c:1724
 [<ffffffff81490788>] shmem_getpage mm/shmem.c:123 [inline]
 [<ffffffff81490788>] shmem_file_read_iter+0x2c8/0xa40 mm/shmem.c:2280
 [<ffffffff815702f7>] vfs_iter_read+0x297/0x3f0 fs/read_write.c:370
 [<ffffffff825cdfa9>] lo_read_simple drivers/block/loop.c:345 [inline]
 [<ffffffff825cdfa9>] do_req_filebacked drivers/block/loop.c:545 [inline]
 [<ffffffff825cdfa9>] loop_handle_cmd drivers/block/loop.c:1698 [inline]
 [<ffffffff825cdfa9>] loop_queue_work+0x14f9/0x2320 drivers/block/loop.c:1710
 [<ffffffff8119d439>] kthread_worker_fn+0x249/0x6b0 kernel/kthread.c:627
 [<ffffffff8119d05d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff839f8e9c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff880184278000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 17624 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 17624 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329