[syzbot] [net?] WARNING in rt_set_nexthop

[syzbot <syzbot+97bf275720e06ad75f63@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    d7b8f8e20813 Linux 6.16-rc5
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=107f9582580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f6cfc97245100778
dashboard link: https://syzkaller.appspot.com/bug?extid=97bf275720e06ad75f63
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17b6728c580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=12aac28c580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/147c9de5b1eb/disk-d7b8f8e2.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f6b4ca03edae/vmlinux-d7b8f8e2.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0c7e75a248fb/bzImage-d7b8f8e2.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97bf275720e06ad75f63@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 5851 at kernel/softirq.c:387 __local_bh_enable_ip+0x180/0x1c0 kernel/softirq.c:387
Modules linked in:
CPU: 0 UID: 0 PID: 5851 Comm: krxrpcio/7001 Not tainted 6.16.0-rc5-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:__local_bh_enable_ip+0x180/0x1c0 kernel/softirq.c:387
Code: 48 3b 44 24 48 75 57 48 8d 65 e0 5b 41 5c 41 5e 41 5f 5d e9 ed 9f 8a ff cc 90 0f 0b 90 e9 f9 fe ff ff e8 53 00 00 00 eb 9f 90 <0f> 0b 90 e9 24 ff ff ff 48 c7 c1 30 17 a2 8f 80 e1 07 80 c1 03 38
RSP: 0018:ffffc9000403f4c0 EFLAGS: 00010046
RAX: 0000000000000000 RBX: 0000000000000201 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000201 RDI: ffffffff89de65e3
RBP: ffffc9000403f548 R08: ffff8880b863bf03 R09: 1ffff110170c77e0
R10: dffffc0000000000 R11: ffffed10170c77e1 R12: ffff8880b863bf00
R13: ffff888076c09570 R14: dffffc0000000000 R15: 1ffff92000807e98
FS:  0000000000000000(0000) GS:ffff888125c1d000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000563736fd8000 CR3: 00000000738cd000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 spin_unlock_bh include/linux/spinlock.h:396 [inline]
 rt_add_uncached_list net/ipv4/route.c:1526 [inline]
 rt_set_nexthop+0x693/0xa80 net/ipv4/route.c:-1
 __mkroute_output net/ipv4/route.c:2669 [inline]
 ip_route_output_key_hash_rcu+0x18f6/0x23a0 net/ipv4/route.c:2864
 ip_route_output_key_hash+0x1b9/0x2e0 net/ipv4/route.c:2694
 __ip_route_output_key include/net/route.h:169 [inline]
 ip_route_output_flow+0x2a/0x150 net/ipv4/route.c:2921
 ip_route_output_ports include/net/route.h:213 [inline]
 rxrpc_assess_MTU_size net/rxrpc/peer_object.c:174 [inline]
 rxrpc_init_peer+0x50a/0xc60 net/rxrpc/peer_object.c:281
 rxrpc_new_incoming_peer+0x281/0x5a0 net/rxrpc/peer_object.c:325
 rxrpc_alloc_incoming_call net/rxrpc/call_accept.c:284 [inline]
 rxrpc_new_incoming_call+0x612/0x14f0 net/rxrpc/call_accept.c:377
 rxrpc_input_packet net/rxrpc/io_thread.c:310 [inline]
 rxrpc_io_thread+0x18b2/0x2cd0 net/rxrpc/io_thread.c:482
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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