===============================
[ INFO: suspicious RCU usage. ]
4.4.174+ #4 Not tainted
-------------------------------
net/ipv6/ip6_fib.c:1465 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 1, debug_locks = 0
7 locks held by syz-executor.5/17260:
 #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff8149a6b6>] file_start_write include/linux/fs.h:2543 [inline]
 #0:  (sb_writers#4){.+.+.+}, at: [<ffffffff8149a6b6>] do_sendfile+0x8a6/0xba0 fs/read_write.c:1228
 #1:  (&sb->s_type->i_mutex_key#9){+.+.+.}, at: [<ffffffff816334ac>] ext4_file_write_iter+0x15c/0xc70 fs/ext4/file.c:116
 #2:  (&(&ei->i_raw_lock)->rlock){+.+...}, at: [<ffffffff81652f61>] spin_lock include/linux/spinlock.h:302 [inline]
 #2:  (&(&ei->i_raw_lock)->rlock){+.+...}, at: [<ffffffff81652f61>] ext4_do_update_inode fs/ext4/inode.c:4632 [inline]
 #2:  (&(&ei->i_raw_lock)->rlock){+.+...}, at: [<ffffffff81652f61>] ext4_mark_iloc_dirty+0x1d1/0x24d0 fs/ext4/inode.c:5190
 #3:  (((&net->ipv6.ip6_fib_timer))){+.-...}, at: [<ffffffff8125822e>] lockdep_copy_map include/linux/lockdep.h:165 [inline]
 #3:  (((&net->ipv6.ip6_fib_timer))){+.-...}, at: [<ffffffff8125822e>] call_timer_fn+0xde/0x850 kernel/time/timer.c:1175
 #4:  (fib6_gc_lock){+.-...}, at: [<ffffffff825fa33a>] spin_lock_bh include/linux/spinlock.h:307 [inline]
 #4:  (fib6_gc_lock){+.-...}, at: [<ffffffff825fa33a>] fib6_run_gc+0x3a/0x230 net/ipv6/ip6_fib.c:1811
 #5:  (rcu_read_lock){......}, at: [<ffffffff825f1ee0>] __fib6_clean_all+0x0/0x240 net/ipv6/ip6_fib.c:1698
 #6:  (&tb->tb6_lock){++--..}, at: [<ffffffff825f1fc8>] __fib6_clean_all+0xe8/0x240 net/ipv6/ip6_fib.c:1712

stack backtrace:
CPU: 1 PID: 17260 Comm: syz-executor.5 Not tainted 4.4.174+ #4
 0000000000000000 3953fd47610aec67 ffff8801db707940 ffffffff81aad1a1
 ffff8801d6acddc0 0000000000000000 0000000000000001 00000000000005b9
 ffff8801b50b2f80 ffff8801db707970 ffffffff813ab7d6 ffff8801db707b90
Call Trace:
 <IRQ>  [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ>  [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff813ab7d6>] lockdep_rcu_suspicious.cold+0x10a/0x149 kernel/locking/lockdep.c:4305
 [<ffffffff825f9ada>] fib6_del+0x7ea/0xae0 net/ipv6/ip6_fib.c:1465
 [<ffffffff825fa06c>] fib6_clean_node+0x29c/0x500 net/ipv6/ip6_fib.c:1652
 [<ffffffff825f1830>] fib6_walk_continue+0x3e0/0x630 net/ipv6/ip6_fib.c:1578
 [<ffffffff825f1d71>] fib6_walk+0x91/0xe0 net/ipv6/ip6_fib.c:1623
 [<ffffffff825f1ea8>] fib6_clean_tree+0xe8/0x120 net/ipv6/ip6_fib.c:1697
 [<ffffffff825f1fe0>] __fib6_clean_all+0x100/0x240 net/ipv6/ip6_fib.c:1713
 [<ffffffff825fa3af>] fib6_clean_all net/ipv6/ip6_fib.c:1724 [inline]
 [<ffffffff825fa3af>] fib6_run_gc+0xaf/0x230 net/ipv6/ip6_fib.c:1821
 [<ffffffff825fa54d>] fib6_gc_timer_cb+0x1d/0x30 net/ipv6/ip6_fib.c:1836
 [<ffffffff812582dd>] call_timer_fn+0x18d/0x850 kernel/time/timer.c:1185
 [<ffffffff81258ebf>] __run_timers kernel/time/timer.c:1261 [inline]
 [<ffffffff81258ebf>] run_timer_softirq+0x51f/0xb70 kernel/time/timer.c:1444
 [<ffffffff8271bb16>] __do_softirq+0x226/0xa3f kernel/softirq.c:273
 [<ffffffff810e1a8a>] invoke_softirq kernel/softirq.c:350 [inline]
 [<ffffffff810e1a8a>] irq_exit+0x10a/0x150 kernel/softirq.c:391
 [<ffffffff8271b24e>] exiting_irq arch/x86/include/asm/apic.h:652 [inline]
 [<ffffffff8271b24e>] smp_apic_timer_interrupt+0x7e/0xb0 arch/x86/kernel/apic/apic.c:926
 [<ffffffff8271a59d>] apic_timer_interrupt+0x9d/0xb0 arch/x86/entry/entry_64.S:768
 <EOI>  [<ffffffff812d4c5f>] ? from_kuid+0x5f/0x240 kernel/user_namespace.c:259
 [<ffffffff8165303f>] i_uid_read include/linux/fs.h:835 [inline]
 [<ffffffff8165303f>] ext4_do_update_inode fs/ext4/inode.c:4641 [inline]
 [<ffffffff8165303f>] ext4_mark_iloc_dirty+0x2af/0x24d0 fs/ext4/inode.c:5190
 [<ffffffff816557d6>] ext4_mark_inode_dirty+0x3f6/0xbf0 fs/ext4/inode.c:5306
 [<ffffffff81664c03>] ext4_dirty_inode+0x73/0xa0 fs/ext4/inode.c:5337
 [<ffffffff815255ee>] __mark_inode_dirty+0x15e/0x1360 fs/fs-writeback.c:2055
 [<ffffffff81544889>] mark_inode_dirty include/linux/fs.h:1948 [inline]
 [<ffffffff81544889>] generic_write_end+0xf9/0x1c0 fs/buffer.c:2124
 [<ffffffff8165fd73>] ext4_da_write_end+0x483/0xd70 fs/ext4/inode.c:2921
 [<ffffffff813b9536>] generic_perform_write+0x326/0x540 mm/filemap.c:2602
 [<ffffffff813bd0b0>] __generic_file_write_iter+0x350/0x540 mm/filemap.c:2716
 [<ffffffff8163384d>] ext4_file_write_iter+0x4fd/0xc70 fs/ext4/file.c:171
 [<ffffffff81496220>] vfs_iter_write+0x1d0/0x3f0 fs/read_write.c:364
 [<ffffffff81534731>] iter_file_splice_write+0x5c1/0xb30 fs/splice.c:1024
 [<ffffffff81530c16>] do_splice_from fs/splice.c:1128 [inline]
 [<ffffffff81530c16>] direct_splice_actor+0x126/0x1a0 fs/splice.c:1294
 [<ffffffff8153252e>] splice_direct_to_actor+0x2ce/0x850 fs/splice.c:1247
 [<ffffffff81532c55>] do_splice_direct+0x1a5/0x260 fs/splice.c:1337
 [<ffffffff8149a2fd>] do_sendfile+0x4ed/0xba0 fs/read_write.c:1229
 [<ffffffff8149c317>] SYSC_sendfile64 fs/read_write.c:1290 [inline]
 [<ffffffff8149c317>] SyS_sendfile64+0x137/0x150 fs/read_write.c:1276
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a
audit: type=1326 audit(1550513679.281:43): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17668 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513680.101:44): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17668 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513681.571:45): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17766 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513682.541:46): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17825 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513683.421:47): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17877 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513684.281:48): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17926 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513685.111:49): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=17968 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513686.091:50): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=18010 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513686.961:51): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=18034 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0
audit: type=1326 audit(1550513687.781:52): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=18056 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45ac8a code=0x0