[v6.1] INFO: rcu detected stall in ppp_ioctl (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c2fda4b3f577 Linux 6.1.156
git tree: linux-6.1.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1722b5e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7eb38bd5021fec61
dashboard link: https://syzkaller.appspot.com/bug?extid=d4cfac02fd23688f95e2
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/784c9646ac1f/disk-c2fda4b3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f509a4777d20/vmlinux-c2fda4b3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ee626a19480c/bzImage-c2fda4b3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d4cfac...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { P8498 0-.... } 2656 jiffies s: 27197 root: 0x1/T
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 8510 Comm: syz.8.1173 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:trace_lock_acquire include/trace/events/lock.h:24 [inline]
RIP: 0010:lock_acquire+0x3d9/0x490 kernel/locking/lockdep.c:5633
Code: c1 ee 06 4a 8d 3c f5 e8 67 1f 8e be 08 00 00 00 e8 4c 09 6e 00 4c 0f a3 25 cc 72 bc 0c 0f 83 1e fd ff ff 65 ff 05 1f 7a 9f 7e <48> c7 c0 40 46 0b 8e 48 c1 e8 03 42 80 3c 38 00 74 0c 48 c7 c7 40
RSP: 0018:ffffc90000007220 EFLAGS: 00000007
RAX: 0000000000000001 RBX: 0000000000000000 RCX: ffffffff8162f514
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff8e1f67e8
RBP: ffffc90000007328 R08: dffffc0000000000 R09: fffffbfff1c3ecfe
R10: fffffbfff1c3ecfe R11: 1ffffffff1c3ecfd R12: 0000000000000000
R13: 1ffff92000000e50 R14: 0000000000000000 R15: dffffc0000000000
FS: 00007fcae98226c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000020000000cf3d CR3: 00000000751fe000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
__perf_output_begin kernel/events/ring_buffer.c:163 [inline]
perf_output_begin_forward+0xb5/0xa80 kernel/events/ring_buffer.c:272
__perf_event_output kernel/events/core.c:7732 [inline]
perf_event_output_forward+0x179/0x2a0 kernel/events/core.c:7750
__perf_event_overflow+0x448/0x610 kernel/events/core.c:9496
perf_tp_event+0x335/0xb60 kernel/events/core.c:10029
perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10002
perf_trace_preemptirq_template+0x287/0x330 include/trace/events/preemptirq.h:14
trace_irq_enable_rcuidle+0xd3/0x140 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x24/0x40 kernel/trace/trace_preemptirq.c:44
asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:rcu_read_unlock_special+0x84/0x500 kernel/rcu/tree_plugin.h:685
Code: f1 f1 f1 00 f2 f2 f2 4a 89 04 2b 66 42 c7 44 2b 09 f3 f3 42 c6 44 2b 0b f3 65 44 8b 35 3d 97 96 7e 41 f7 c6 00 00 f0 00 74 45 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 66 42 c7 44 2b
RSP: 0018:ffffc90000007aa0 EFLAGS: 00000206
RAX: 474dbff7bb35fe00 RBX: 1ffff92000000f5c RCX: 474dbff7bb35fe00
RDX: dffffc0000000000 RSI: ffffffff8a8c0500 RDI: ffffffff8adef020
RBP: ffffc90000007b90 R08: dffffc0000000000 R09: fffffbfff215c44a
R10: fffffbfff215c44a R11: 1ffffffff215c449 R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3b900 R15: 0000000000000001
__rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:823 [inline]
ieee80211_iterate_active_interfaces_atomic+0x156/0x170 net/mac80211/util.c:826
mac80211_hwsim_beacon+0xb7/0x1b0 drivers/net/wireless/mac80211_hwsim.c:2147
__run_hrtimer kernel/time/hrtimer.c:1747 [inline]
__hrtimer_run_queues+0x554/0xd60 kernel/time/hrtimer.c:1811
hrtimer_run_softirq+0x183/0x2a0 kernel/time/hrtimer.c:1828
handle_softirqs+0x2a1/0x920 kernel/softirq.c:596
__do_softirq kernel/softirq.c:630 [inline]
invoke_softirq kernel/softirq.c:470 [inline]
__irq_exit_rcu+0x12f/0x220 kernel/softirq.c:679
irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xa5/0x100 kernel/locking/spinlock.c:194
Code: 74 05 e8 1e 71 65 f7 48 c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f6 44 24 21 02 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 46 fc 35 f7 65 8b 05 47 b5 e0 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc900047b7340 EFLAGS: 00000206
RAX: 474dbff7bb35fe00 RBX: 0000000000000a02 RCX: 474dbff7bb35fe00
RDX: dffffc0000000000 RSI: ffffffff8a8c0500 RDI: 0000000000000001
RBP: ffffc900047b73c8 R08: dffffc0000000000 R09: fffffbfff215c44a
R10: fffffbfff215c44a R11: 1ffffffff215c449 R12: dffffc0000000000
R13: ffff888044a8c000 R14: ffffffff96e9f208 R15: 1ffff920008f6e68
__debug_check_no_obj_freed lib/debugobjects.c:988 [inline]
debug_check_no_obj_freed+0x515/0x530 lib/debugobjects.c:1009
free_pages_prepare mm/page_alloc.c:1465 [inline]
free_pcp_prepare mm/page_alloc.c:1509 [inline]
free_unref_page_prepare+0x2a6/0x9a0 mm/page_alloc.c:3384
free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3479
qlink_free mm/kasan/quarantine.c:168 [inline]
qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
__kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:305
kasan_slab_alloc include/linux/kasan.h:201 [inline]
slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
slab_alloc_node mm/slub.c:3359 [inline]
slab_alloc mm/slub.c:3367 [inline]
__kmem_cache_alloc_lru mm/slub.c:3374 [inline]
kmem_cache_alloc+0x123/0x2f0 mm/slub.c:3383
kmem_cache_zalloc include/linux/slab.h:689 [inline]
__kernfs_new_node+0xd4/0x7d0 fs/kernfs/dir.c:614
kernfs_new_node+0x148/0x250 fs/kernfs/dir.c:690
__kernfs_create_file+0x47/0x2e0 fs/kernfs/file.c:1068
sysfs_add_file_mode_ns+0x234/0x2f0 fs/sysfs/file.c:294
create_files fs/sysfs/group.c:64 [inline]
internal_create_group+0x487/0xce0 fs/sysfs/group.c:148
internal_create_groups fs/sysfs/group.c:188 [inline]
sysfs_create_groups+0x55/0x120 fs/sysfs/group.c:214
device_add_groups drivers/base/core.c:2752 [inline]
device_add_attrs+0xdb/0x800 drivers/base/core.c:2900
device_add+0x64b/0xfb0 drivers/base/core.c:3648
netdev_register_kobject+0x176/0x310 net/core/net-sysfs.c:2013
register_netdevice+0x12b9/0x1aa0 net/core/dev.c:10204
ppp_unit_register drivers/net/ppp/ppp_generic.c:1229 [inline]
ppp_dev_configure+0x874/0xad0 drivers/net/ppp/ppp_generic.c:1285
ppp_create_interface drivers/net/ppp/ppp_generic.c:3362 [inline]
ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:1070 [inline]
ppp_ioctl+0x65f/0x1940 drivers/net/ppp/ppp_generic.c:743
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fcae898eec9
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:00007fcae9822038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fcae8be5fa0 RCX: 00007fcae898eec9
RDX: 000000110c230000 RSI: 00000000c004743e RDI: 000000000000000b
RBP: 00007fcae8a11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fcae8be6038 R14: 00007fcae8be5fa0 R15: 00007ffe31521d58
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup