INFO: rcu detected stall in ppp_ioctl

Status: upstream: reported on 2026/06/20 19:57
Reported-by: syzbot+9f8b83525aa87d5697f2@syzkaller.appspotmail.com
First crash: 57d, last: 57d
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 INFO: rcu detected stall in ppp_ioctl (3) 1 1 107d 107d 0/3 auto-obsoleted due to no activity on 2026/08/09 22:48
linux-5.15 INFO: rcu detected stall in ppp_ioctl 1 1 236d 236d 0/3 auto-obsoleted due to no activity on 2026/04/02 20:21
linux-6.1 INFO: rcu detected stall in ppp_ioctl 1 1 685d 685d 0/3 auto-obsoleted due to no activity on 2025/01/09 16:14
upstream INFO: rcu detected stall in ppp_ioctl mm 1 3 642d 657d 0/29 auto-obsoleted due to no activity on 2025/02/10 18:41
linux-6.1 INFO: rcu detected stall in ppp_ioctl (2) 1 1 305d 305d 0/3 auto-obsoleted due to no activity on 2026/01/24 16:32
android-5-15 BUG: soft lockup in ppp_ioctl 1 5 722d 849d 0/2 auto-obsoleted due to no activity on 2024/11/22 22:02

Sample crash report:
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-....: (10497 ticks this GP) idle=9ed4/1/0x4000000000000000 softirq=40831/40831 fqs=5118
rcu: 	         hardirqs   softirqs   csw/system
rcu: 	 number:  1429874          0            0
rcu: 	cputime:    13915      38564           36   ==> 52480(ms)
rcu: 	(t=10500 jiffies g=49753 q=327 ncpus=2)
CPU: 1 PID: 12890 Comm: syz.3.2157 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5758
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc900001f04a0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 75842e7145608700
RDX: 0000000000000000 RSI: ffffffff8acadce0 RDI: ffffffff8b1c7be0
RBP: ffffc900001f05b0 R08: dffffc0000000000 R09: 1ffffffff22378a0
R10: dffffc0000000000 R11: fffffbfff22378a1 R12: 1ffff9200003e0a0
R13: ffffffff8d131da0 R14: 0000000000000246 R15: dffffc0000000000
FS:  00007fae8ec006c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd7e67cda8 CR3: 000000002ed94000 CR4: 00000000003506e0
DR0: 0000200000000300 DR1: 0000200000000300 DR2: 0000200000000300
DR3: 0000200000000300 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 is_bpf_text_address+0x47/0x2a0 kernel/bpf/core.c:741
 kernel_text_address+0xa0/0xd0 kernel/extable.c:125
 __kernel_text_address+0xd/0x30 kernel/extable.c:79
 unwind_get_return_address+0x5d/0xc0 arch/x86/kernel/unwind_orc.c:369
 arch_stack_walk+0x11d/0x190 arch/x86/kernel/stacktrace.c:26
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 kmem_cache_alloc_node+0x1af/0x310 mm/slub.c:3540
 __alloc_skb+0x103/0x2c0 net/core/skbuff.c:643
 alloc_skb include/linux/skbuff.h:1316 [inline]
 nlmsg_new include/net/netlink.h:1010 [inline]
 __neigh_notify+0x15c/0x300 net/core/neighbour.c:3532
 neigh_update_notify net/core/neighbour.c:2680 [inline]
 neigh_timer_handler+0xb05/0xff0 net/core/neighbour.c:1169
 call_timer_fn+0x189/0x540 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x570/0x810 kernel/time/timer.c:2023
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x27d/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:preempt_schedule_irq+0xba/0x150 kernel/sched/core.c:7010
Code: 00 00 43 c6 44 37 04 f8 74 0b 0f 0b 48 f7 03 08 00 00 00 74 6f bf 01 00 00 00 e8 01 48 d0 f6 e8 3c 34 01 f7 fb bf 01 00 00 00 <e8> 31 b4 ff ff 43 c6 44 37 08 00 48 c7 44 24 40 00 00 00 00 9c 8f
RSP: 0018:ffffc90019766f20 EFLAGS: 00000282
RAX: 75842e7145608700 RBX: 0000000000000000 RCX: 75842e7145608700
RDX: dffffc0000000000 RSI: ffffffff8acacb60 RDI: 0000000000000001
RBP: ffffc90019766fc0 R08: ffffffff911bc50f R09: 1ffffffff22378a1
R10: dffffc0000000000 R11: fffffbfff22378a2 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff920032ecde4
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_acquire+0x208/0x420 kernel/locking/lockdep.c:5758
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 f0 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 43 c7 44 3c 08 00 00 00 00 65 48 8b 04 25
RSP: 0018:ffffc90019767080 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 75842e7145608700
RDX: 0000000000000000 RSI: ffffffff8acadce0 RDI: ffffffff8b1c7be0
RBP: ffffc90019767190 R08: dffffc0000000000 R09: 1ffffffff22378a0
R10: dffffc0000000000 R11: fffffbfff22378a1 R12: 1ffff920032ece1c
R13: ffffffff8d131da0 R14: 0000000000000246 R15: dffffc0000000000
 rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
 rcu_read_lock include/linux/rcupdate.h:786 [inline]
 is_bpf_text_address+0x47/0x2a0 kernel/bpf/core.c:741
 kernel_text_address+0xa0/0xd0 kernel/extable.c:125
 __kernel_text_address+0xd/0x30 kernel/extable.c:79
 unwind_get_return_address+0x5d/0xc0 arch/x86/kernel/unwind_orc.c:369
 arch_stack_walk+0x11d/0x190 arch/x86/kernel/stacktrace.c:26
 stack_trace_save+0xaa/0x100 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x17e/0x2c0 mm/slub.c:3519
 kmem_cache_zalloc include/linux/slab.h:711 [inline]
 __kernfs_new_node+0xe5/0x7f0 fs/kernfs/dir.c:624
 kernfs_new_node+0x14c/0x260 fs/kernfs/dir.c:700
 __kernfs_create_file+0x4b/0x2e0 fs/kernfs/file.c:1068
 sysfs_add_file_mode_ns+0x237/0x2f0 fs/sysfs/file.c:294
 create_files fs/sysfs/group.c:64 [inline]
 internal_create_group+0x431/0xd10 fs/sysfs/group.c:152
 internal_create_groups fs/sysfs/group.c:192 [inline]
 sysfs_create_groups+0x59/0x120 fs/sysfs/group.c:218
 device_add_groups drivers/base/core.c:2786 [inline]
 device_add_attrs+0xdf/0x830 drivers/base/core.c:2895
 device_add+0x51a/0xc40 drivers/base/core.c:3639
 netdev_register_kobject+0x188/0x320 net/core/net-sysfs.c:2042
 register_netdevice+0x12aa/0x1ba0 net/core/dev.c:10318
 ppp_unit_register drivers/net/ppp/ppp_generic.c:1232 [inline]
 ppp_dev_configure+0x850/0xad0 drivers/net/ppp/ppp_generic.c:1288
 ppp_create_interface drivers/net/ppp/ppp_generic.c:3365 [inline]
 ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:1073 [inline]
 ppp_ioctl+0xa78/0x1ac0 drivers/net/ppp/ppp_generic.c:743
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fae8dd9ce59
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:00007fae8ec00028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fae8e015fa0 RCX: 00007fae8dd9ce59
RDX: 000000110e22fff7 RSI: 00000000c004743e RDI: 0000000000000003
RBP: 00007fae8de32e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fae8e016038 R14: 00007fae8e015fa0 R15: 00007ffdcf83f5f8
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/20 19:56 linux-6.6.y d1cfde2d5d15 43bfcdb0 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in ppp_ioctl
* Struck through repros no longer work on HEAD.