[v6.6] INFO: rcu detected stall in schedule

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Dec 26, 2025, 8:29:20 AM (3 days ago) Dec 26
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Hello,

syzbot found the following issue on:

HEAD commit: 5fa4793a2d2d Linux 6.6.119
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1592489a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=691a6769a86ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=e7e189c7eec4630d0e81
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/857fe583cdec/disk-5fa4793a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ed4d3c1402bc/vmlinux-5fa4793a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/40296d968c3d/bzImage-5fa4793a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e7e189...@syzkaller.appspotmail.com

bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P6475/1:b..l
rcu: (detected by 0, t=10503 jiffies, g=14041, q=394 ncpus=2)
task:syz.0.168 state:R running task stack:25832 pid:6475 ppid:5770 flags:0x00004006
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5380 [inline]
__schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
preempt_schedule_common+0x82/0xc0 kernel/sched/core.c:6866
preempt_schedule+0xab/0xc0 kernel/sched/core.c:6890
preempt_schedule_thunk+0x1a/0x30 arch/x86/entry/thunk_64.S:45
htab_unlock_bucket kernel/bpf/hashtab.c:180 [inline]
htab_map_update_elem+0xe83/0x1040 kernel/bpf/hashtab.c:1197
bpf_map_update_value+0x660/0x720 kernel/bpf/syscall.c:203
generic_map_update_batch+0x5e0/0x810 kernel/bpf/syscall.c:1800
bpf_map_do_batch+0x3d7/0x610 kernel/bpf/syscall.c:5007
__sys_bpf+0x31b/0x800 kernel/bpf/syscall.c:-1
__do_sys_bpf kernel/bpf/syscall.c:5577 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5575 [inline]
__x64_sys_bpf+0x7c/0x90 kernel/bpf/syscall.c:5575
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fd4c1f8f749
RSP: 002b:00007fd4c2d60038 EFLAGS: 00000246 ORIG_RAX: 0000000000000141
RAX: ffffffffffffffda RBX: 00007fd4c21e5fa0 RCX: 00007fd4c1f8f749
RDX: 0000000000000038 RSI: 0000200000000200 RDI: 000000000000001a
RBP: 00007fd4c2013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd4c21e6038 R14: 00007fd4c21e5fa0 R15: 00007ffd41406208
</TASK>
rcu: rcu_preempt kthread starved for 10526 jiffies! g14041 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->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:R running task stack:25896 pid:17 ppid:2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5380 [inline]
__schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
schedule+0xbd/0x170 kernel/sched/core.c:6773
schedule_timeout+0x160/0x280 kernel/time/timer.c:2168
rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
rcu_gp_kthread+0x99/0x380 kernel/rcu/tree.c:1866
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 0 PID: 18 Comm: migration/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Stopper: 0x0 <- 0x0
RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_switch+0xb0/0x120 kernel/kcov.c:350
Code: c8 74 77 4e 8b 54 ce 10 65 44 8b 1d b2 1f 7e 7e 41 81 e3 00 01 ff 00 74 13 41 81 fb 00 01 00 00 75 d9 41 83 b8 1c 16 00 00 00 <74> cf 45 8b 98 f8 15 00 00 41 83 fb 03 75 c2 4d 8b 98 00 16 00 00
RSP: 0000:ffffc900000069b0 EFLAGS: 00000246
RAX: 0000000000000003 RBX: ffffffff8f4921a2 RCX: 0000000000000003
RDX: ffffffff813aba19 RSI: ffffffff8cb9e7e0 RDI: 0000000000000001
RBP: ffffc90000006af8 R08: ffff88801ba59e00 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000100 R12: ffffc90000006aa8
R13: dffffc0000000000 R14: 0000000000000001 R15: ffffffff8f4921a6
FS: 0000000000000000(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2daba8 CR3: 0000000061eee000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
unwind_next_frame+0x16d9/0x2970 arch/x86/kernel/unwind_orc.c:641
arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:328
kasan_slab_alloc include/linux/kasan.h:188 [inline]
slab_post_alloc_hook+0x6e/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+0x11e/0x2e0 mm/slub.c:3519
skb_clone+0x1eb/0x370 net/core/skbuff.c:1915
dev_queue_xmit_nit+0x24d/0xbb0 net/core/dev.c:2340
xmit_one net/core/dev.c:3615 [inline]
dev_hard_start_xmit+0x148/0x740 net/core/dev.c:3635
__dev_queue_xmit+0x1a64/0x35a0 net/core/dev.c:4425
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
hsr_xmit net/hsr/hsr_forward.c:380 [inline]
hsr_forward_do net/hsr/hsr_forward.c:471 [inline]
hsr_forward_skb+0x1317/0x2120 net/hsr/hsr_forward.c:624
hsr_dev_xmit+0x1e7/0x350 net/hsr/hsr_device.c:238
__netdev_start_xmit include/linux/netdevice.h:4943 [inline]
netdev_start_xmit include/linux/netdevice.h:4957 [inline]
xmit_one net/core/dev.c:3619 [inline]
dev_hard_start_xmit+0x246/0x740 net/core/dev.c:3635
__dev_queue_xmit+0x1a64/0x35a0 net/core/dev.c:4425
neigh_output include/net/neighbour.h:543 [inline]
ip6_finish_output2+0xe2e/0x1650 net/ipv6/ip6_output.c:141
dst_output include/net/dst.h:467 [inline]
NF_HOOK include/linux/netfilter.h:304 [inline]
ndisc_send_skb+0xbed/0x14b0 net/ipv6/ndisc.c:513
addrconf_rs_timer+0x2bc/0x600 net/ipv6/addrconf.c:4006
call_timer_fn+0x16e/0x530 kernel/time/timer.c:1701
expire_timers kernel/time/timer.c:1752 [inline]
__run_timers+0x52d/0x7d0 kernel/time/timer.c:2023
run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
handle_softirqs+0x280/0x820 kernel/softirq.c:578
__do_softirq kernel/softirq.c:612 [inline]
invoke_softirq kernel/softirq.c:452 [inline]
__irq_exit_rcu+0xc7/0x190 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:get_current arch/x86/include/asm/current.h:41 [inline]
RIP: 0010:preempt_latency_start kernel/sched/core.c:5828 [inline]
RIP: 0010:preempt_count_add+0x9e/0x1a0 kernel/sched/core.c:5851
Code: 65 8b 05 1d 48 a8 7e 25 ff ff ff 7f 39 f8 75 42 48 8b 5c 24 18 48 89 df e8 6f c9 0c 00 85 c0 74 09 31 db 31 ff e8 62 c9 0c 00 <65> 4c 8b 35 ea 47 a8 7e 49 81 c6 c8 14 00 00 4c 89 f0 48 c1 e8 03
RSP: 0000:ffffc90000177e08 EFLAGS: 00000246
RAX: 0000000000000000 RBX: ffffffff8a6fb516 RCX: ffffffff96e9b400
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff8a6fb516
RBP: 0000000000000000 R08: ffffffff8e4a212f R09: 1ffffffff1c94425
R10: dffffc0000000000 R11: fffffbfff1c94426 R12: ffff88801ba5b568
R13: 1ffff1100374b6ad R14: 1ffff1100374b3c0 R15: dffffc0000000000
schedule+0xb6/0x170 kernel/sched/core.c:6772
smpboot_thread_fn+0x710/0xa00 kernel/smpboot.c:160
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>
net_ratelimit: 2 callbacks suppressed
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
net_ratelimit: 8 callbacks suppressed
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on veth0_to_bridge with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:1b, vlan:0)
bridge0: received packet on bridge_slave_0 with own address as source address (addr:aa:aa:aa:aa:aa:0c, vlan:0)


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