Re: [syzbot] [net?] WARNING in rcu_note_context_switch (5)

[syzbot <syzbot+84d4a405ed798b40c96d@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    b73bc9ca3686 Merge tag 'nf-next-26-07-02' of https://git.k..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1043ef19580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5c4196ba0e33631d
dashboard link: https://syzkaller.appspot.com/bug?extid=84d4a405ed798b40c96d
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11d07719580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1443ef19580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b7f8c662a498/disk-b73bc9ca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d3ffbd688a32/vmlinux-b73bc9ca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/235149e2b678/bzImage-b73bc9ca.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+84d4a405ed798b40c96d@syzkaller.appspotmail.com

------------[ cut here ]------------
Voluntary context switch within RCU read-side critical section!
WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0xc58/0xef0 kernel/rcu/tree_plugin.h:332, CPU#1: syz.0.17/5817
Modules linked in:
CPU: 1 UID: 0 PID: 5817 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:rcu_note_context_switch+0xc58/0xef0 kernel/rcu/tree_plugin.h:332
Code: 00 41 c6 45 00 00 48 8b 3d 35 15 ab 0e 48 81 c4 a8 00 00 00 5b 41 5c 41 5d 41 5e 41 5f 5d e9 af 60 ff ff 48 8d 3d c8 d6 ae 0e <67> 48 0f b9 3a e9 6f f4 ff ff 90 0f 0b 90 45 84 e4 0f 84 3e f4 ff
RSP: 0018:ffffc90002eced20 EFLAGS: 00010002
RAX: 0000000000000000 RBX: ffff888030d80000 RCX: 0000000080000002
RDX: 0000000000000000 RSI: ffffffff8c4bd260 RDI: ffffffff905ad640
RBP: dffffc0000000000 R08: ffffffff905767f7 R09: 1ffffffff20aecfe
R10: dffffc0000000000 R11: fffffbfff20aecff R12: 0000000000000000
R13: dffffc0000000000 R14: ffff8880b873c180 R15: ffff888030d804c4
FS:  000055557f679500(0000) GS:ffff888125060000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff0e1073780 CR3: 0000000022684000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __schedule+0x2e9/0x56c0 kernel/sched/core.c:7088
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 netlink_broadcast_filtered+0xe53/0xea0 net/netlink/af_netlink.c:1553
 nlmsg_multicast_filtered include/net/netlink.h:1165 [inline]
 nlmsg_multicast include/net/netlink.h:1184 [inline]
 nlmsg_notify+0xe3/0x1a0 net/netlink/af_netlink.c:2599
 __ip6_del_rt_siblings+0x5ed/0x7d0 net/ipv6/route.c:4080
 ip6_route_del+0x104f/0x1100 net/ipv6/route.c:4220
 inet6_rtm_delroute+0x5d7/0x6d0 net/ipv6/route.c:5657
 rtnetlink_rcv_msg+0x802/0xc00 net/core/rtnetlink.c:7076
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x7bb/0x940 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1900
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmsg net/socket.c:2770 [inline]
 __do_sys_sendmsg net/socket.c:2775 [inline]
 __se_sys_sendmsg net/socket.c:2773 [inline]
 __x64_sys_sendmsg+0x1b1/0x290 net/socket.c:2773
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7ff0e119de59
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:00007ffd842e7d98 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007ff0e1425fa0 RCX: 00007ff0e119de59
RDX: 0000000000000000 RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007ff0e1233e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff0e1425fac R14: 00007ff0e1425fa0 R15: 00007ff0e1425fa0
 </TASK>
----------------
Code disassembly (best guess):
   0:	00 41 c6             	add    %al,-0x3a(%rcx)
   3:	45 00 00             	add    %r8b,(%r8)
   6:	48 8b 3d 35 15 ab 0e 	mov    0xeab1535(%rip),%rdi        # 0xeab1542
   d:	48 81 c4 a8 00 00 00 	add    $0xa8,%rsp
  14:	5b                   	pop    %rbx
  15:	41 5c                	pop    %r12
  17:	41 5d                	pop    %r13
  19:	41 5e                	pop    %r14
  1b:	41 5f                	pop    %r15
  1d:	5d                   	pop    %rbp
  1e:	e9 af 60 ff ff       	jmp    0xffff60d2
  23:	48 8d 3d c8 d6 ae 0e 	lea    0xeaed6c8(%rip),%rdi        # 0xeaed6f2
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	e9 6f f4 ff ff       	jmp    0xfffff4a3
  34:	90                   	nop
  35:	0f 0b                	ud2
  37:	90                   	nop
  38:	45 84 e4             	test   %r12b,%r12b
  3b:	0f                   	.byte 0xf
  3c:	84 3e                	test   %bh,(%rsi)
  3e:	f4                   	hlt
  3f:	ff                   	.byte 0xff


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