[syzbot] [net?] possible deadlock in rlb_choose_channel (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c21b90f77687 x86/CPU/AMD: Prevent improper isolation of sh..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10ec7dba580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4caf64b1ee83dac0
dashboard link: https://syzkaller.appspot.com/bug?extid=1db58dbbccbf93c65c83
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/2f3edabe3b67/disk-c21b90f7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/539b63753e79/vmlinux-c21b90f7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/48e6e7cbc4ca/bzImage-c21b90f7.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+1db58d...@syzkaller.appspotmail.com

ip6_tunnel: ip6tnl1 xmit: Local address not yet configured!
ip6_tunnel: ip6tnl1 xmit: Local address not yet configured!
============================================
WARNING: possible recursive locking detected
syzkaller #0 Tainted: G L
--------------------------------------------
kworker/u8:3/47 is trying to acquire lock:
ffff88807a618e98 (&bond->mode_lock){+.-.}-{3:3}, at: spin_lock include/linux/spinlock.h:342 [inline]
ffff88807a618e98 (&bond->mode_lock){+.-.}-{3:3}, at: rlb_choose_channel+0x37/0x19a0 drivers/net/bonding/bond_alb.c:562

but task is already holding lock:
ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: rlb_update_rx_clients drivers/net/bonding/bond_alb.c:466 [inline]
ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: bond_alb_monitor+0xe8a/0x17e0 drivers/net/bonding/bond_alb.c:1618

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&bond->mode_lock);
lock(&bond->mode_lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

7 locks held by kworker/u8:3/47:
#0: ffff8880516b7140 ((wq_completion)bond5#2){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3277 [inline]
#0: ffff8880516b7140 ((wq_completion)bond5#2){+.+.}-{0:0}, at: process_scheduled_works+0xa35/0x1860 kernel/workqueue.c:3385
#1: ffffc90000b77c40 ((work_completion)(&(&bond->alb_work)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3278 [inline]
#1: ffffc90000b77c40 ((work_completion)(&(&bond->alb_work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa70/0x1860 kernel/workqueue.c:3385
#2: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#2: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
#2: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: bond_alb_monitor+0xf8/0x17e0 drivers/net/bonding/bond_alb.c:1546
#3: ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:348 [inline]
#3: ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: rlb_update_rx_clients drivers/net/bonding/bond_alb.c:466 [inline]
#3: ffff88807ffa0e98 (&bond->mode_lock){+.-.}-{3:3}, at: bond_alb_monitor+0xe8a/0x17e0 drivers/net/bonding/bond_alb.c:1618
#4: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#4: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
#4: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: arp_xmit+0x23/0x270 net/ipv4/arp.c:663
#5: ffffffff8e95cdc0 (rcu_read_lock_bh){....}-{1:3}, at: local_bh_disable include/linux/bottom_half.h:20 [inline]
#5: ffffffff8e95cdc0 (rcu_read_lock_bh){....}-{1:3}, at: rcu_read_lock_bh include/linux/rcupdate.h:891 [inline]
#5: ffffffff8e95cdc0 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x2b6/0x3950 net/core/dev.c:4791
#6: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#6: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
#6: ffffffff8e95cd60 (rcu_read_lock){....}-{1:3}, at: bond_start_xmit+0xb4/0x1900 drivers/net/bonding/bond_main.c:5591

stack backtrace:
CPU: 0 UID: 0 PID: 47 Comm: kworker/u8:3 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: bond5 bond_alb_monitor
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_deadlock_bug+0x279/0x290 kernel/locking/lockdep.c:3041
check_deadlock kernel/locking/lockdep.c:3093 [inline]
validate_chain kernel/locking/lockdep.c:3895 [inline]
__lock_acquire+0x253f/0x2cf0 kernel/locking/lockdep.c:5237
lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868
__raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
spin_lock include/linux/spinlock.h:342 [inline]
rlb_choose_channel+0x37/0x19a0 drivers/net/bonding/bond_alb.c:562
rlb_arp_xmit drivers/net/bonding/bond_alb.c:680 [inline]
bond_xmit_alb_slave_get+0x1071/0x20a0 drivers/net/bonding/bond_alb.c:1493
bond_alb_xmit+0x24/0x40 drivers/net/bonding/bond_alb.c:1528
__bond_start_xmit drivers/net/bonding/bond_main.c:5569 [inline]
bond_start_xmit+0x6a2/0x1900 drivers/net/bonding/bond_main.c:5593
__netdev_start_xmit include/linux/netdevice.h:5368 [inline]
netdev_start_xmit include/linux/netdevice.h:5377 [inline]
xmit_one net/core/dev.c:3888 [inline]
dev_hard_start_xmit+0x2cd/0x830 net/core/dev.c:3904
__dev_queue_xmit+0x14d9/0x3950 net/core/dev.c:4870
NF_HOOK+0x33a/0x3c0 include/linux/netfilter.h:-1
arp_xmit+0x16c/0x270 net/ipv4/arp.c:665
rlb_update_client+0x2a8/0x6b0 drivers/net/bonding/bond_alb.c:455
rlb_update_rx_clients drivers/net/bonding/bond_alb.c:473 [inline]
bond_alb_monitor+0xf6a/0x17e0 drivers/net/bonding/bond_alb.c:1618
process_one_work kernel/workqueue.c:3302 [inline]
process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3385
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3466
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


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