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

From: syzbot <[email-masked]>
Date: Fri, 26 Dec 2025 08:54:21 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    9448598b22c5 Linux 6.19-rc2
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11423b1a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a11e0f726bfb6765
dashboard link: https://syzkaller.appspot.com/bug?extid=84d4a405ed798b40c96d
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-9448598b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e6328e25c1c8/vmlinux-9448598b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d1590b31d26d/bzImage-9448598b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

------------[ cut here ]------------
Voluntary context switch within RCU read-side critical section!
WARNING: kernel/rcu/tree_plugin.h:332 at rcu_note_context_switch+0x104/0x1de0 kernel/rcu/tree_plugin.h:332, CPU#0: syz.2.13843/20505
Modules linked in:
CPU: 0 UID: 0 PID: 20505 Comm: syz.2.13843 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:rcu_note_context_switch+0x104/0x1de0 kernel/rcu/tree_plugin.h:332
Code: 0f b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 bb 10 00 00 8b 85 84 04 00 00 85 c0 7e 0c 48 8d 3d 9c 94 e7 0e <67> 48 0f b9 3a 65 48 8b 2d 57 0e 0e 12 48 8d bd 84 04 00 00 48 b8
RSP: 0018:ffffc9000410f028 EFLAGS: 00010002
RAX: 0000000000000001 RBX: ffff88806a43bc40 RCX: ffffffff81a41b2f
RDX: 0000000000000000 RSI: ffffffff8bf2b380 RDI: ffffffff908c3650
RBP: ffff888054ce24c0 R08: 0000000000000000 R09: fffffbfff211169a
R10: ffffffff9088b4d7 R11: ffff888054ce2ff0 R12: 0000000000000000
R13: ffff888054ce24c0 R14: ffffffff9088e574 R15: ffff88806a43ac80
FS:  00007f883fff66c0(0000) GS:ffff8880d68f5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000004a53a000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 __schedule+0x2dc/0x6150 kernel/sched/core.c:6748
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 netlink_broadcast_filtered+0x96d/0xf90 net/netlink/af_netlink.c:1547
 nlmsg_multicast_filtered include/net/netlink.h:1165 [inline]
 nlmsg_multicast include/net/netlink.h:1184 [inline]
 nlmsg_notify+0x9e/0x220 net/netlink/af_netlink.c:2593
 __ip6_del_rt_siblings net/ipv6/route.c:4056 [inline]
 ip6_route_del+0x115c/0x1d70 net/ipv6/route.c:4196
 inet6_rtm_delroute+0x27c/0x3b0 net/ipv6/route.c:5629
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6958
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x5aa/0x870 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x8c8/0xdd0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:727 [inline]
 __sock_sendmsg net/socket.c:742 [inline]
 ____sys_sendmsg+0xa5d/0xc30 net/socket.c:2592
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2646
 __sys_sendmsg+0x16d/0x220 net/socket.c:2678
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f8841d8f7c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f883fff6038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f8841fe5fa0 RCX: 00007f8841d8f7c9
RDX: 0000000000000000 RSI: 0000200000000280 RDI: 0000000000000003
RBP: 00007f8841e13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8841fe6038 R14: 00007f8841fe5fa0 R15: 00007fffea27ccb8
 </TASK>
----------------
Code disassembly (best guess):
   0:	0f b6 14 02          	movzbl (%rdx,%rax,1),%edx
   4:	48 89 f8             	mov    %rdi,%rax
   7:	83 e0 07             	and    $0x7,%eax
   a:	83 c0 03             	add    $0x3,%eax
   d:	38 d0                	cmp    %dl,%al
   f:	7c 08                	jl     0x19
  11:	84 d2                	test   %dl,%dl
  13:	0f 85 bb 10 00 00    	jne    0x10d4
  19:	8b 85 84 04 00 00    	mov    0x484(%rbp),%eax
  1f:	85 c0                	test   %eax,%eax
  21:	7e 0c                	jle    0x2f
  23:	48 8d 3d 9c 94 e7 0e 	lea    0xee7949c(%rip),%rdi        # 0xee794c6
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	65 48 8b 2d 57 0e 0e 	mov    %gs:0x120e0e57(%rip),%rbp        # 0x120e0e8e
  36:	12
  37:	48 8d bd 84 04 00 00 	lea    0x484(%rbp),%rdi
  3e:	48                   	rex.W
  3f:	b8                   	.byte 0xb8

---
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