=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
include/net/nexthop.h:319 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
3 locks held by syz.0.3447/17319:
 #0: ffff88807a82d690 (nlk_cb_mutex-ROUTE){+.+.}-{3:3}, at: __netlink_dump_start+0xf5/0x720 net/netlink/af_netlink.c:2363
 #1: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x9/0x30 include/linux/rcupdate.h:313
 #2: ffff88805fb94830 (&tb->tb6_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:369 [inline]
 #2: ffff88805fb94830 (&tb->tb6_lock){+...}-{2:2}, at: fib6_dump_table+0x1ce/0x5b0 net/ipv6/ip6_fib.c:587

stack backtrace:
CPU: 0 PID: 17319 Comm: syz.0.3447 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nexthop_mpath_fill_node include/net/nexthop.h:319 [inline]
 rt6_fill_node_nexthop+0x2cc/0x600 net/ipv6/route.c:5594
 rt6_fill_node+0x109e/0x1a40 net/ipv6/route.c:5756
 rt6_dump_route+0x592/0xa70 net/ipv6/route.c:5926
 fib6_dump_node+0xa2/0x250 net/ipv6/ip6_fib.c:521
 fib6_walk_continue+0x662/0x8b0 net/ipv6/ip6_fib.c:2118
 fib6_walk+0x149/0x270 net/ipv6/ip6_fib.c:2166
 fib6_dump_table+0x1da/0x5b0 net/ipv6/ip6_fib.c:588
 inet6_dump_fib+0x6bc/0xa60 net/ipv6/ip6_fib.c:702
 netlink_dump+0x6d2/0xdd0 net/netlink/af_netlink.c:2291
 __netlink_dump_start+0x4e4/0x720 net/netlink/af_netlink.c:2398
 netlink_dump_start include/linux/netlink.h:260 [inline]
 rtnetlink_rcv_msg+0xd91/0xf10 net/core/rtnetlink.c:5654
 netlink_rcv_skb+0x1e9/0x430 net/netlink/af_netlink.c:2519
 netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
 netlink_unicast+0x78f/0x940 net/netlink/af_netlink.c:1340
 netlink_sendmsg+0x8ba/0xbe0 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:706 [inline]
 __sock_sendmsg net/socket.c:718 [inline]
 sock_write_iter+0x2a6/0x3a0 net/socket.c:1090
 call_write_iter include/linux/fs.h:2173 [inline]
 new_sync_write fs/read_write.c:507 [inline]
 vfs_write+0x748/0xd70 fs/read_write.c:594
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7fda8f8b50d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 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 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fda8db0d028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fda8fb3cfa0 RCX: 00007fda8f8b50d9
RDX: 0000000000000024 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007fda8f94c024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fda8fb3d038 R14: 00007fda8fb3cfa0 R15: 00007fff1f8f9648
 </TASK>