[syzbot] [net?] [mm?] INFO: rcu detected stall in rescuer_thread (2)

[syzbot <syzbot+d5f7a5097c24c7c2dbbb@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    b1d9154878ce Merge branch 'net-mlx5e-shampo-fixes-for-64kb..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=15cc5bcd980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=e46b8a1c645465a9
dashboard link: https://syzkaller.appspot.com/bug?extid=d5f7a5097c24c7c2dbbb
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=134820b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bef31d61ceb8/disk-b1d91548.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/67c31be6c377/vmlinux-b1d91548.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7b9f62743e14/bzImage-b1d91548.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d5f7a5097c24c7c2dbbb@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	(detected by 0, t=12991 jiffies, g=11121, q=1246 ncpus=2)
rcu: All QSes seen, last rcu_preempt kthread activity 3112 (4294972946-4294969834), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 3112 jiffies! g11121 f0x2 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:27288 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5325 [inline]
 __schedule+0x1798/0x4cc0 kernel/sched/core.c:6929
 __schedule_loop kernel/sched/core.c:7011 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:7026
 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 6005 Comm: kworker/R-wg-cr Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: wg-crypt-wg2 wg_packet_tx_worker
RIP: 0010:rb_erase+0xb/0xe60 lib/rbtree.c:441
Code: ca 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 41 57 41 56 41 55 <41> 54 53 48 83 ec 28 48 89 f3 49 89 fd 48 b9 00 00 00 00 00 fc ff
RSP: 0018:ffffc90000a08ce0 EFLAGS: 00000046
RAX: 0000000000000000 RBX: ffff8880b8927c90 RCX: ffff88801f7a5ac0
RDX: 0000000000010000 RSI: ffff8880b8927c90 RDI: ffff88807de66340
RBP: 1ffff1100fbccc68 R08: ffffffff8f7cdc77 R09: 1ffffffff1ef9b8e
R10: dffffc0000000000 R11: fffffbfff1ef9b8f R12: ffff8880b8927c98
R13: dffffc0000000000 R14: ffff88807de66340 R15: 1ffff11017124f93
FS:  0000000000000000(0000) GS:ffff88812623c000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056323a462a38 CR3: 000000002891e000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 rb_erase_cached include/linux/rbtree.h:126 [inline]
 timerqueue_del+0xae/0x100 lib/timerqueue.c:57
 __remove_hrtimer kernel/time/hrtimer.c:1114 [inline]
 __run_hrtimer kernel/time/hrtimer.c:1757 [inline]
 __hrtimer_run_queues+0x364/0xc60 kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1041 [inline]
 __sysvec_apic_timer_interrupt+0x10b/0x410 arch/x86/kernel/apic/apic.c:1058
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1052
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:queued_write_lock_slowpath+0x125/0x260 kernel/locking/qrwlock.c:85
Code: 00 01 00 00 43 0f b6 04 27 84 c0 74 35 89 d9 80 e1 07 80 c1 03 38 c1 7c 29 48 89 df e8 e4 b8 dc f6 eb 1f f3 90 43 0f b6 04 27 <84> c0 74 14 89 d9 80 e1 07 80 c1 03 38 c1 7c 08 48 89 df e8 c3 b8
RSP: 0018:ffffc90003337300 EFLAGS: 00000206
RAX: 0000000000000000 RBX: ffffffff8f3dd900 RCX: ffffffff8b490058
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffffff8f3dd900
RBP: ffffc900033373b0 R08: ffffffff8f3dd903 R09: 1ffffffff1e7bb20
R10: dffffc0000000000 R11: fffffbfff1e7bb21 R12: dffffc0000000000
R13: 1ffff92000666e64 R14: ffffc90003337350 R15: 1ffffffff1e7bb20
 queued_write_lock include/asm-generic/qrwlock.h:101 [inline]
 do_raw_write_lock+0x1f2/0x260 kernel/locking/spinlock_debug.c:211
 ___neigh_create+0xe81/0x2260 net/core/neighbour.c:690
 ip6_finish_output2+0x1175/0x1480 net/ipv6/ip6_output.c:128
 NF_HOOK_COND include/linux/netfilter.h:307 [inline]
 ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247
 ip6tunnel_xmit include/net/ip6_tunnel.h:162 [inline]
 udp_tunnel6_xmit_skb+0x68d/0xb30 net/ipv6/ip6_udp_tunnel.c:112
 send6+0x5ac/0x8d0 drivers/net/wireguard/socket.c:152
 wg_socket_send_skb_to_peer+0x111/0x1d0 drivers/net/wireguard/socket.c:178
 wg_packet_create_data_done drivers/net/wireguard/send.c:251 [inline]
 wg_packet_tx_worker+0x1c8/0x7c0 drivers/net/wireguard/send.c:276
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 rescuer_thread+0x53c/0xdd0 kernel/workqueue.c:3523
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>


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