syzbot


INFO: rcu detected stall in ppp_release

Status: upstream: reported on 2026/02/08 05:49
Reported-by: syzbot+4f10c36460cda5d1824c@syzkaller.appspotmail.com
First crash: 1d20h, last: 1d20h
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in ppp_release mm 1 1 203d 203d 0/29 auto-obsoleted due to no activity on 2025/10/19 12:31
android-5-15 BUG: soft lockup in ppp_release 1 1 655d 655d 0/2 auto-obsoleted due to no activity on 2024/07/24 06:05

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 1-.... } 2657 jiffies s: 1329 root: 0x2/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4476 Comm: syz.4.32 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:__wrmsr arch/x86/include/asm/msr.h:94 [inline]
RIP: 0010:native_apic_msr_eoi_write+0x0/0x10 arch/x86/include/asm/apic.h:211
Code: 74 08 4c 89 f7 e8 f0 4b 9b 00 49 8b 06 bf f0 03 00 00 89 de 5b 41 5e 41 5f ff e0 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 <b9> 0b 08 00 00 31 c0 31 d2 0f 30 c3 0f 1f 40 00 81 ff cf 00 00 00
RSP: 0018:ffffc900001e09b8 EFLAGS: 00000046
RAX: 1ffffffff18c9f66 RBX: ffffffff8c64fb30 RCX: 7ff2d9632412e100
RDX: 1ffffffff1f41208 RSI: 0000000000000000 RDI: 00000000000000b0
RBP: 0000000000000000 R08: ffffffff8fa09048 R09: ffffffff8fa09058
R10: ffffffff8fa09050 R11: ffffffff8fa09043 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 0000000000000000
FS:  00007f9a10d2b6c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fbb02617dac CR3: 0000000058d5e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 apic_eoi arch/x86/include/asm/apic.h:399 [inline]
 ack_APIC_irq arch/x86/include/asm/apic.h:445 [inline]
 __sysvec_irq_work+0x53/0x350 arch/x86/kernel/irq_work.c:19
 instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
 sysvec_irq_work+0x4a/0xc0 arch/x86/kernel/irq_work.c:17
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:rcu_read_unlock_special+0x7f/0x510 kernel/rcu/tree_plugin.h:685
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 92 31 95 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc900001e0aa0 EFLAGS: 00000206
RAX: 7ff2d9632412e100 RBX: 1ffff9200003c15c RCX: 7ff2d9632412e100
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0d20
RBP: ffffc900001e0b90 R08: ffffffff90af424f R09: 1ffffffff215e849
R10: dffffc0000000000 R11: fffffbfff215e84a R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8f3b900 R15: 0000000000000002
 __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+0x560/0xd70 kernel/time/hrtimer.c:1811
 hrtimer_run_softirq+0x183/0x2a0 kernel/time/hrtimer.c:1828
 handle_softirqs+0x2a1/0x930 kernel/softirq.c:596
 __do_softirq kernel/softirq.c:630 [inline]
 invoke_softirq kernel/softirq.c:470 [inline]
 __irq_exit_rcu+0x13b/0x230 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:finish_task_switch+0x26a/0x8f0 kernel/sched/core.c:5124
Code: 0f 84 3b 01 00 00 48 85 db 0f 85 5a 01 00 00 0f 1f 44 00 00 4c 8b 75 d0 4c 89 e7 e8 d0 fd dc 08 e8 eb 2c 2f 00 fb 4c 8b 65 c0 <49> 8d bc 24 f8 15 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 28 84 c0
RSP: 0018:ffffc90004a2f6d8 EFLAGS: 00000286
RAX: 7ff2d9632412e100 RBX: 0000000000000000 RCX: 7ff2d9632412e100
RDX: dffffc0000000000 RSI: ffffffff8a8c1220 RDI: ffffffff8adf0d20
RBP: ffffc90004a2f730 R08: ffffffff90af424f R09: 1ffffffff215e849
R10: dffffc0000000000 R11: fffffbfff215e84a R12: ffff8880302b1dc0
R13: dffffc0000000000 R14: ffff888026770000 R15: ffff8880b8f3b5d0
 context_switch kernel/sched/core.c:5248 [inline]
 __schedule+0x11d9/0x40e0 kernel/sched/core.c:6562
 preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6874
 irqentry_exit+0x63/0x70 kernel/entry/common.c:439
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:fib_netdev_event+0x5e/0x470 net/ipv4/fib_frontend.c:1487
Code: 0b f9 49 8b 1f 4c 8d b3 50 06 00 00 e8 4b 29 65 01 4c 89 f0 48 c1 e8 03 42 80 3c 28 00 74 08 4c 89 f7 e8 35 ed 0b f9 4d 8b 36 <bf> 06 00 00 00 4c 89 e6 e8 55 05 bb f8 49 83 fc 06 75 24 e8 6a 01
RSP: 0018:ffffc90004a2fa50 EFLAGS: 00000246
RAX: 1ffff11004cf0cca RBX: ffff888026786000 RCX: ffff8880302b1dc0
RDX: ffffc9000f4fa000 RSI: 000000000001ad9c RDI: 000000000001ad9d
RBP: 0000000000000000 R08: ffffffff90af424f R09: 1ffffffff215e849
R10: dffffc0000000000 R11: fffffbfff215e84a R12: 0000000000000006
R13: dffffc0000000000 R14: ffff888059ca3880 R15: ffffc90004a2fb80
 notifier_call_chain kernel/notifier.c:87 [inline]
 raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
 call_netdevice_notifiers_extack net/core/dev.c:2052 [inline]
 call_netdevice_notifiers net/core/dev.c:2066 [inline]
 unregister_netdevice_many+0x1086/0x1930 net/core/dev.c:11003
 unregister_netdevice_queue+0x324/0x370 net/core/dev.c:10934
 unregister_netdevice include/linux/netdevice.h:3075 [inline]
 ppp_release+0xec/0x1f0 drivers/net/ppp/ppp_generic.c:420
 __fput+0x22c/0x920 fs/file_table.c:320
 task_work_run+0x1d0/0x260 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f9a0fd9aeb9
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:00007f9a10d2b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: fffffffffffffff2 RBX: 00007f9a10016090 RCX: 00007f9a0fd9aeb9
RDX: 000000110c230041 RSI: 00000000c004743e RDI: 0000000000000008
RBP: 00007f9a0fe08c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9a10016128 R14: 00007f9a10016090 R15: 00007ffc90354e78
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/08 05:48 linux-6.1.y 0182cb5b74ee 4c131dc4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in ppp_release
* Struck through repros no longer work on HEAD.