[syzbot] [mm?] [kernfs?] INFO: rcu detected stall in netlink_sendmsg (6)

[syzbot] [mm?] [kernfs?] INFO: rcu detected stall in netlink_sendmsg (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    9c88929cc18c Merge branch 'vxlan-fixes-for-skb-header-pull..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=12e316b9580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4e38b15c29e6a1d9
dashboard link: https://syzkaller.appspot.com/bug?extid=508388c85f7a82cbd79e
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=113de499580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13c10aea580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c839a5778222/disk-9c88929c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7d9c12119e13/vmlinux-9c88929c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f0189c8f6aad/bzImage-9c88929c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+508388c85f7a82cbd79e@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 1, t=10502 jiffies, g=15149, q=760 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4294966187-4294955685), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g15149 f0x2 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:27496 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x17d9/0x56c0 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7326
 schedule_timeout+0x152/0x2c0 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x30c/0x11f0 kernel/rcu/tree.c:2123
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2325
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </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: 5666 Comm: syz-executor142 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:__lock_is_held kernel/locking/lockdep.c:5601 [inline]
RIP: 0010:lock_is_held_type+0x89/0x150 kernel/locking/lockdep.c:5940
Code: 9c 07 41 83 bd 98 0b 00 00 00 7e 48 4c 89 eb 48 81 c3 a0 0b 00 00 45 31 ff 49 83 ff 31 73 24 48 89 df 4c 89 f6 e8 f7 01 00 00 <85> c0 75 2a 49 ff c7 49 63 85 98 0b 00 00 48 83 c3 28 49 39 c7 7c
RSP: 0018:ffffc90000007d68 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff88807e8aaaf0 RCX: 0000000000010001
RDX: ffff88807e8a9f00 RSI: ffff8880b86281d8 RDI: ffff88807e8aaaf0
RBP: 00000000ffffffff R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000000fac R12: 0000000000000046
R13: ffff88807e8a9f00 R14: ffff8880b86281d8 R15: 0000000000000002
FS:  0000555577b834c0(0000) GS:ffff888124f50000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7bc378eef0 CR3: 0000000070652000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 lock_is_held include/linux/lockdep.h:249 [inline]
 enqueue_hrtimer+0x79/0x2c0 kernel/time/hrtimer.c:1107
 __run_hrtimer kernel/time/hrtimer.c:2048 [inline]
 __hrtimer_run_queues+0x4ce/0xa10 kernel/time/hrtimer.c:2096
 hrtimer_interrupt+0x448/0x910 kernel/time/hrtimer.c:2215
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1051 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x430 arch/x86/kernel/apic/apic.c:1068
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1062 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1062
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:__orc_find arch/x86/kernel/unwind_orc.c:101 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:238 [inline]
RIP: 0010:unwind_next_frame+0x4d0/0x2550 arch/x86/kernel/unwind_orc.c:510
Code: fc ff df 4c 8b 7c 24 10 49 8d 6e 38 0f 84 8a 16 00 00 e9 ee 01 00 00 49 89 d5 49 89 d7 4c 89 e0 4c 29 f8 48 89 c1 48 c1 f9 02 <48> c1 e8 3f 48 01 c8 48 83 e0 fe 49 8d 1c 47 48 89 d8 48 c1 e8 03
RSP: 0018:ffffc90003ace660 EFLAGS: 00000202
RAX: 0000000000000008 RBX: ffffffff9073eec0 RCX: 0000000000000002
RDX: ffffffff9073eeb4 RSI: ffffffff90f35a48 RDI: ffffffff8c4bdb20
RBP: ffffffff81b1f9a8 R08: 0000000000000007 R09: 0000000000000000
R10: 0000000000000000 R11: ffffffff8eb59c60 R12: ffffffff9073eebc
R13: ffffffff9073eeb4 R14: ffffc90003ace708 R15: ffffffff9073eeb4
 arch_stack_walk+0x11b/0x150 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa9/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4612 [inline]
 slab_alloc_node mm/slub.c:4945 [inline]
 kmem_cache_alloc_noprof+0x2a0/0x5f0 mm/slub.c:4959
 __kernfs_new_node+0xe6/0x980 fs/kernfs/dir.c:665
 kernfs_new_node fs/kernfs/dir.c:751 [inline]
 kernfs_create_dir_ns+0xfe/0x230 fs/kernfs/dir.c:1120
 sysfs_create_dir_ns+0x12f/0x2a0 fs/sysfs/dir.c:59
 create_dir lib/kobject.c:73 [inline]
 kobject_add_internal+0x622/0xcd0 lib/kobject.c:240
 kobject_add_varg lib/kobject.c:374 [inline]
 kobject_add+0x163/0x240 lib/kobject.c:426
 device_add+0x3fa/0xb80 drivers/base/core.c:3695
 netdev_register_kobject+0x178/0x310 net/core/net-sysfs.c:2337
 register_netdevice+0x1433/0x1eb0 net/core/dev.c:11446
 cfg80211_register_netdevice+0x138/0x2d0 net/wireless/core.c:1690
 ieee80211_if_add+0x108d/0x1600 net/mac80211/iface.c:2397
 ieee80211_register_hw+0x3e79/0x4a50 net/mac80211/main.c:1644
 mac80211_hwsim_new_radio+0x3238/0x5680 drivers/net/wireless/virtual/mac80211_hwsim_main.c:6113
 hwsim_new_radio_nl+0xd8b/0xf90 drivers/net/wireless/virtual/mac80211_hwsim_main.c:6904
 genl_family_rcv_msg_doit+0x233/0x340 net/netlink/genetlink.c:1114
 genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
 genl_rcv_msg+0x614/0x7a0 net/netlink/genetlink.c:1209
 netlink_rcv_skb+0x226/0x4a0 net/netlink/af_netlink.c:2556
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 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_sendto+0x408/0x5a0 net/socket.c:2252
 __do_sys_sendto net/socket.c:2259 [inline]
 __se_sys_sendto net/socket.c:2255 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2255
 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: 0033:0x7f7bc370bc2e
Code: 08 0f 85 25 ed ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 90 41 57 41 56 4d 89 c6 41 55 4d 89 cd 41 54 55 53 48 83 ec 08
RSP: 002b:00007fffcb9d7168 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000555577b834c0 RCX: 00007f7bc370bc2e
RDX: 0000000000000024 RSI: 00007f7bc3791990 RDI: 0000000000000003
RBP: 0000000000000003 R08: 00007fffcb9d71e4 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 0000000000000000 R14: 00007f7bc3791990 R15: 0000000000000000
 </TASK>


---
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