syzbot
INFO: rcu detected stall in sys_sendto (2)
Status:
upstream: reported C repro on 2025/12/12 19:08
Bug presence:
origin:upstream
[Documentation on labels]
Reported-by: syzbot+a036dce33097533fe040@syzkaller.appspotmail.com
First crash: 303d, last: 1d07h
Sample crash report:
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P4409/1:b..l P4387/1:b..l
(detected by 0, t=10502 jiffies, g=11401, q=344 ncpus=2)
task:syz-executor state:R running task stack:22896 pid:4387 ppid:4384 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0x107f/0x4030 kernel/sched/core.c:6563
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6875
irqentry_exit+0x63/0x70 kernel/entry/common.c:442
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:lock_is_held_type+0x13a/0x190 kernel/locking/lockdep.c:5866
Code: 75 40 48 c7 04 24 00 00 00 00 9c 8f 04 24 f7 04 24 00 02 00 00 75 46 41 f7 c5 00 02 00 00 74 01 fb 65 48 8b 04 25 28 00 00 00 <48> 3b 44 24 08 75 3c 89 e8 48 83 c4 10 5b 41 5c 41 5d 41 5e 41 5f
RSP: 0018:ffffc90003fc7a90 EFLAGS: 00000206
RAX: 795797a657ba6400 RBX: ffff88802f2a0000 RCX: 795797a657ba6400
RDX: ffff88802f2a0000 RSI: ffffffff8a8c2b20 RDI: ffffffff8adf71a0
RBP: 0000000000000001 R08: dffffc0000000000 R09: 1ffffffff2326848
R10: dffffc0000000000 R11: fffffbfff2326849 R12: 0000000000000000
R13: 0000000000000246 R14: ffffffff8d92d8a0 R15: ffff88802f2a0ae0
net_generic+0x101/0x240 include/net/netns/generic.h:46
netlink_deliver_tap+0x1f/0x1b0 net/netlink/af_netlink.c:333
netlink_deliver_tap_kernel net/netlink/af_netlink.c:347 [inline]
netlink_unicast_kernel net/netlink/af_netlink.c:1317 [inline]
netlink_unicast+0x777/0x920 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x8ad/0xbd0 net/netlink/af_netlink.c:1877
sock_sendmsg_nosec net/socket.c:718 [inline]
__sock_sendmsg net/socket.c:730 [inline]
__sys_sendto+0x497/0x650 net/socket.c:2153
__do_sys_sendto net/socket.c:2165 [inline]
__se_sys_sendto net/socket.c:2161 [inline]
__x64_sys_sendto+0xda/0xf0 net/socket.c:2161
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: 0033:0x7f84de95ea0e
RSP: 002b:00007ffd9c6ee718 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000555595311500 RCX: 00007f84de95ea0e
RDX: 0000000000000030 RSI: 00007f84df753610 RDI: 0000000000000006
RBP: 0000000000000001 R08: 00007ffd9c6ee794 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000006
R13: 0000000000000000 R14: 00007f84df753610 R15: 0000000000000000
</TASK>
task:kworker/u4:6 state:R running task stack:26320 pid:4409 ppid:2 flags:0x00004000
Workqueue: bat_events batadv_iv_send_outstanding_bat_ogm_packet
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5246 [inline]
__schedule+0x107f/0x4030 kernel/sched/core.c:6563
preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6875
irqentry_exit+0x63/0x70 kernel/entry/common.c:442
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:lock_acquire+0x226/0x4a0 kernel/locking/lockdep.c:5794
Code: f7 84 24 80 00 00 00 00 02 00 00 43 c6 44 3c 04 f8 0f 85 ef 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:ffffc90003297920 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: fcc48457315eba00
RDX: 0000000000000000 RSI: ffffffff8a8c2b20 RDI: ffffffff8adf71a0
RBP: ffffc90003297a28 R08: dffffc0000000000 R09: 1ffffffff2326848
R10: dffffc0000000000 R11: fffffbfff2326849 R12: 1ffff92000652f30
R13: 0000000000000000 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:350 [inline]
rcu_read_lock include/linux/rcupdate.h:791 [inline]
batadv_iv_ogm_slide_own_bcast_window net/batman-adv/bat_iv_ogm.c:769 [inline]
batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:849 [inline]
batadv_iv_ogm_schedule+0x458/0x1080 net/batman-adv/bat_iv_ogm.c:908
batadv_iv_send_outstanding_bat_ogm_packet+0x6e9/0x800 net/batman-adv/bat_iv_ogm.c:1805
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>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10557 jiffies! g11401 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: Possible timer handling issue on cpu=0 timer-softirq=3988
rcu: rcu_preempt kthread starved for 10558 jiffies! g11401 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:26896 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: 0 PID: 4477 Comm: syz.3.20 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
RIP: 0010:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 ae 8b 26 f7 48 89 df e8 16 5e 27 f7 e8 71 b7 4a f7 fb bf 01 00 00 00 <e8> 76 c7 1a f7 65 8b 05 37 77 c4 75 85 c0 74 02 5b c3 e8 44 8b c2
RSP: 0018:ffffc90004167b98 EFLAGS: 00000282
RAX: 271ca2635e60ee00 RBX: ffff88802f2c6f00 RCX: 271ca2635e60ee00
RDX: dffffc0000000000 RSI: ffffffff8a8c19a0 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff88802f2c6f03 R09: 1ffff11005e58de0
R10: dffffc0000000000 R11: ffffed1005e58de1 R12: 0000000000000021
R13: ffff88802f2c7398 R14: dffffc0000000000 R15: 000000001c000004
FS: 000055556aa4d500(0000) GS:ffff8880b8c00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fc3d50700d0 CR3: 000000006b4a3000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
spin_unlock_irq include/linux/spinlock.h:401 [inline]
get_signal+0x114a/0x1340 kernel/signal.c:2887
arch_do_signal_or_restart+0xc4/0x1310 arch/x86/kernel/signal.c:871
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:177
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:213
__syscall_exit_to_user_mode_work kernel/entry/common.c:295 [inline]
syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:306
do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fc3d519e1d9
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:00007ffce91e7cc8 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 00007fc3d5425fa0 RCX: 00007fc3d519e1d9
RDX: 0000200000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007fc3d5235888 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fc3d5425fac R14: 00007fc3d5425fa0 R15: 00007fc3d5425fa0
</TASK>
sched: RT throttling activated
Struck through repros no longer work on HEAD.