syzbot
INFO: rcu detected stall in sys_recvmmsg (4)
Status:
upstream: reported on 2026/04/22 14:30
Reported-by: syzbot+b089ec3c3cd5d4bbd763@syzkaller.appspotmail.com
First crash: 129d, last: 11d
Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-...!: (1 GPs behind) idle=47ac/1/0x4000000000000000 softirq=48198/48199 fqs=7
(detected by 1, t=10502 jiffies, g=63921, q=1208 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 11288 Comm: syz.0.1829 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:hlock_class kernel/locking/lockdep.c:228 [inline]
RIP: 0010:__lock_acquire+0x1151/0x7c40 kernel/locking/lockdep.c:5059
Code: 03 89 c3 81 e3 ff 1f 00 00 c1 e8 03 25 f8 03 00 00 48 8d b8 40 02 b1 90 be 08 00 00 00 e8 b7 4c 6f 00 48 0f a3 1d 7f f2 4c 0f <0f> 83 9a 01 00 00 48 8d 04 5b c1 e0 06 48 8d 98 00 81 49 90 49 b8
RSP: 0018:ffffc900000078a0 EFLAGS: 00000057
RAX: 0000000000000001 RBX: 0000000000000060 RCX: ffffffff81640fb9
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffffffff90b10248
RBP: ffffc90000007ad0 R08: ffffffff90b1024f R09: 1ffffffff2162049
R10: dffffc0000000000 R11: fffffbfff216204a R12: ffff88801b74a8d8
R13: ffff88801b749e00 R14: 000000002ee63bb2 R15: 000000006d47acd1
FS: 00007f13d77d56c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000558e3f588a38 CR3: 0000000072d3b000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<IRQ>
lock_acquire+0x1bb/0x4a0 kernel/locking/lockdep.c:5676
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
_raw_spin_lock_irqsave+0xb0/0x100 kernel/locking/spinlock.c:162
debug_object_activate+0x68/0x4f0 lib/debugobjects.c:747
debug_hrtimer_activate kernel/time/hrtimer.c:448 [inline]
debug_activate kernel/time/hrtimer.c:502 [inline]
enqueue_hrtimer+0x37/0x410 kernel/time/hrtimer.c:1097
__run_hrtimer kernel/time/hrtimer.c:1768 [inline]
__hrtimer_run_queues+0x63e/0xc90 kernel/time/hrtimer.c:1815
hrtimer_interrupt+0x399/0x980 kernel/time/hrtimer.c:1877
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1107 [inline]
__sysvec_apic_timer_interrupt+0x153/0x5a0 arch/x86/kernel/apic/apic.c:1124
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
sysvec_apic_timer_interrupt+0x9b/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:import_iovec+0x74/0xa0 lib/iov_iter.c:1838
Code: e3 02 31 ff 89 de e8 4b a9 6d fd d1 eb 44 89 ef 4c 89 e6 44 89 fa 89 e9 4d 89 f0 4c 8b 0c 24 53 e8 81 fa ff ff 48 83 c4 10 5b <41> 5c 41 5d 41 5e 41 5f 5d c3 89 d9 80 e1 07 80 c1 03 38 c1 7c bd
RSP: 0018:ffffc9000c2b7a50 EFLAGS: 00000286
RAX: 0000000000000000 RBX: ffffc9000c2b7be0 RCX: 0000000000000002
RDX: ffffc9000c2b7d50 RSI: 0000000000000000 RDI: ffffc9000c2b7d48
RBP: 0000000000000008 R08: 0000000000000000 R09: ffffc9000c2b7d30
R10: dffffc0000000000 R11: fffff52001856fb0 R12: 0000000000000000
R13: 0000000000000000 R14: ffffc9000c2b7be0 R15: 0000000000000000
copy_msghdr_from_user net/socket.c:2456 [inline]
recvmsg_copy_msghdr net/socket.c:2704 [inline]
___sys_recvmsg+0x4b2/0x590 net/socket.c:2776
do_recvmmsg+0x370/0x810 net/socket.c:2874
__sys_recvmmsg net/socket.c:2953 [inline]
__do_sys_recvmmsg net/socket.c:2976 [inline]
__se_sys_recvmmsg net/socket.c:2969 [inline]
__x64_sys_recvmmsg+0x195/0x250 net/socket.c:2969
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f13d959e0d9
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:00007f13d77d5028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b
RAX: ffffffffffffffda RBX: 00007f13d9826090 RCX: 00007f13d959e0d9
RDX: 0000000000010106 RSI: 00002000000000c0 RDI: 0000000000000003
RBP: 00007f13d9635024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f13d9826128 R14: 00007f13d9826090 R15: 00007ffec549fc08
</TASK>
rcu: rcu_preempt kthread starved for 10426 jiffies! g63921 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
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:27888 pid:16 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0x107f/0x4030 kernel/sched/core.c:6563
schedule+0xb9/0x180 kernel/sched/core.c:6639
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2168
rcu_gp_fqs_loop+0x303/0x1350 kernel/rcu/tree.c:1706
rcu_gp_kthread+0x99/0x3b0 kernel/rcu/tree.c:1905
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 PID: 57 Comm: kworker/u4:4 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events_unbound toggle_allocation_gate
RIP: 0010:csd_lock_wait kernel/smp.c:424 [inline]
RIP: 0010:smp_call_function_many_cond+0x1148/0x1250 kernel/smp.c:998
Code: 41 8b 1f 89 de 83 e6 01 31 ff e8 73 ff 0a 00 83 e3 01 48 bb 00 00 00 00 00 fc ff df 75 0a e8 ff fb 0a 00 e9 34 ff ff ff f3 90 <41> 0f b6 04 1c 84 c0 75 14 41 f7 07 01 00 00 00 0f 84 17 ff ff ff
RSP: 0018:ffffc90001587800 EFLAGS: 00000293
RAX: ffffffff81773243 RBX: dffffc0000000000 RCX: ffff88801ea89e00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90001587960 R08: ffffffff90b10247 R09: 1ffffffff2162048
R10: dffffc0000000000 R11: fffffbfff2162049 R12: 1ffff110171c8641
R13: ffff8880b8f3bdc0 R14: 0000000000000000 R15: ffff8880b8e43208
FS: 0000000000000000(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000558e3f5af1b8 CR3: 000000000c88e000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
on_each_cpu_cond_mask+0x3b/0x80 kernel/smp.c:1165
on_each_cpu include/linux/smp.h:71 [inline]
text_poke_sync arch/x86/kernel/alternative.c:1574 [inline]
text_poke_bp_batch+0x5ae/0x850 arch/x86/kernel/alternative.c:1836
text_poke_flush arch/x86/kernel/alternative.c:1965 [inline]
text_poke_finish+0x16/0x30 arch/x86/kernel/alternative.c:1972
arch_jump_label_transform_apply+0x13/0x20 arch/x86/kernel/jump_label.c:146
static_key_enable_cpuslocked+0x11f/0x240 kernel/jump_label.c:207
static_key_enable+0x16/0x20 kernel/jump_label.c:220
toggle_allocation_gate+0xba/0x470 mm/kfence/core.c:821
process_one_work+0x8ab/0x1160 kernel/workqueue.c:2292
worker_thread+0xaf5/0x12a0 kernel/workqueue.c:2439
kthread+0x29d/0x330 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
</TASK>
Struck through repros no longer work on HEAD.