Message-ID: <69619005.050a0220.1c677c.03d8.GAE@google.com>
Date: Fri, 09 Jan 2026 15:32:21 -0800
From: syzbot <syzbot+3ad87d519fc52afbb1d5@...kaller.appspotmail.com>
To: davem@...emloft.net, edumazet@...gle.com, horms@...nel.org, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: [syzbot] [net?] INFO: rcu detected stall in netlink_recvmsg (5)

Hello,

syzbot found the following issue on:

HEAD commit:    3609fa95fb0f Merge tag 'devicetree-fixes-for-6.19-2' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15552f92580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a11e0f726bfb6765
dashboard link: https://syzkaller.appspot.com/bug?extid=3ad87d519fc52afbb1d5
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13552f92580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1394ae9a580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/92a7817c3585/disk-3609fa95.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b0243ba76e7b/vmlinux-3609fa95.xz
kernel image: https://storage.googleapis.com/syzbot-assets/61a47c574b87/bzImage-3609fa95.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+3ad87d519fc52afbb1d5@...kaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5191/1:b.el
rcu: 	(detected by 1, t=10502 jiffies, g=11677, q=274 ncpus=2)
task:udevd           state:R  running task     stack:26472 pid:5191  tgid:5191  ppid:1      task_flags:0x400140 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 preempt_schedule_irq+0x51/0x90 kernel/sched/core.c:7190
 irqentry_exit+0x1d8/0x8c0 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:kasan_byte_accessible+0x18/0x30 mm/kasan/generic.c:212
Code: 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 b8 00 00 00 00 00 fc ff df 48 c1 ef 03 48 01 c7 0f b6 07 <3c> 07 0f 96 c0 c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f
RSP: 0018:ffffc90003a474a0 EFLAGS: 00000286
RAX: 0000000000000000 RBX: ffffffff8e3c96a0 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff816cb681 RDI: fffffbfff1c792d4
RBP: ffffffff8e3c96a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000083b41 R12: ffffffff816cb681
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 __kasan_check_byte+0x13/0x50 mm/kasan/common.c:573
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire kernel/locking/lockdep.c:5842 [inline]
 lock_acquire+0xfc/0x330 kernel/locking/lockdep.c:5825
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 class_rcu_constructor include/linux/rcupdate.h:1195 [inline]
 unwind_next_frame+0xd1/0x20b0 arch/x86/kernel/unwind_orc.c:495
 arch_stack_walk+0x94/0x100 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0x8e/0xc0 kernel/stacktrace.c:122
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free mm/slub.c:6670 [inline]
 kmem_cache_free+0x2d8/0x770 mm/slub.c:6781
 kfree_skbmem+0x1a4/0x1f0 net/core/skbuff.c:1130
 __kfree_skb net/core/skbuff.c:1197 [inline]
 consume_skb net/core/skbuff.c:1428 [inline]
 consume_skb+0xcc/0x100 net/core/skbuff.c:1422
 netlink_recvmsg+0x5b9/0xa90 net/netlink/af_netlink.c:1972
 sock_recvmsg_nosec net/socket.c:1078 [inline]
 sock_recvmsg+0x1f9/0x250 net/socket.c:1100
 ____sys_recvmsg+0x218/0x6b0 net/socket.c:2812
 ___sys_recvmsg+0x114/0x1a0 net/socket.c:2854
 __sys_recvmsg+0x16a/0x220 net/socket.c:2887
 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: 0033:0x7fd6b22a7407
RSP: 002b:00007fff89341350 EFLAGS: 00000202 ORIG_RAX: 000000000000002f
RAX: ffffffffffffffda RBX: 00007fd6b2aae880 RCX: 00007fd6b22a7407
RDX: 0000000000000000 RSI: 00007fff893413e0 RDI: 0000000000000004
RBP: 0000000000000001 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055ce9df56d80
R13: 00007fff893414a0 R14: 00007fff893413ec R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10547 jiffies! g11677 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:28584 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 schedule_timeout+0x123/0x290 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x1ea/0xaf0 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x26d/0x380 kernel/rcu/tree.c:2285
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:82
Code: c6 5f 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 13 49 12 00 fb f4 <e9> cc 35 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0000:ffffffff8e007df8 EFLAGS: 000002c6
RAX: 0000000000138781 RBX: 0000000000000000 RCX: ffffffff8b7816d9
RDX: 0000000000000000 RSI: ffffffff8dace4f3 RDI: ffffffff8bf2b480
RBP: fffffbfff1c12f68 R08: 0000000000000001 R09: ffffed101708673d
R10: ffff8880b84339eb R11: ffffffff8e098670 R12: 0000000000000000
R13: ffffffff8e097b40 R14: ffffffff9088b9d0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881248f5000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000001f76b000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000410
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:191 [inline]
 do_idle+0x38d/0x510 kernel/sched/idle.c:332
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:430
 rest_init+0x16b/0x2b0 init/main.c:757
 start_kernel+0x3ef/0x4d0 init/main.c:1206
 x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x148
 </TASK>


---
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