Re: [syzbot] [lvs?] BUG: sleeping function called from invalid context in ip_vs_conn_expire

Jiayuan Chen
2026-04-14T12:09:32Z

On 4/14/26 6:30 PM, syzbot wrote:

[...]

> if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+504e778ddaecd36fdd17@syzkaller.appspotmail.com
>
> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48

The problem occurs under PREEMPT_RT. conn_tab_lock pair with spin_lock
has the problem:

conn_tab_lock(...) -> hlist_bl_lock -> preempt_disable()  ==>
disables preemption
spin_lock(&cp->lock) -> rt_mutex  ==> sleepable under RT, but
preemption is already disabled by conn_tab_lock

> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 16, name: ktimers/0
> preempt_count: 2, expected: 0
> RCU nest depth: 3, expected: 3
> 8 locks held by ktimers/0/16:
> #0: ffffffff8de5f260 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
> #1: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
> #2: ffff8880b8826360 (&base->expiry_lock){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
> #2: ffff8880b8826360 (&base->expiry_lock){+...}-{3:3}, at: timer_base_lock_expiry kernel/time/timer.c:1502 [inline]
> #2: ffff8880b8826360 (&base->expiry_lock){+...}-{3:3}, at: __run_timer_base+0x120/0x9f0 kernel/time/timer.c:2384
> #3: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
> #3: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
> #3: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
> #3: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
> #4: ffffc90000157a80 ((&cp->timer)){+...}-{0:0}, at: call_timer_fn+0xd4/0x5e0 kernel/time/timer.c:1745
> #5: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
> #5: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
> #5: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: ip_vs_conn_unlink net/netfilter/ipvs/ip_vs_conn.c:315 [inline]
> #5: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: ip_vs_conn_expire+0x257/0x2390 net/netfilter/ipvs/ip_vs_conn.c:1260
> #6: ffffffff8de5f260 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
> #7: ffff888068d4c3f0 (&cp->lock#2){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
> #7: ffff888068d4c3f0 (&cp->lock#2){+...}-{3:3}, at: ip_vs_conn_unlink net/netfilter/ipvs/ip_vs_conn.c:324 [inline]
> #7: ffff888068d4c3f0 (&cp->lock#2){+...}-{3:3}, at: ip_vs_conn_expire+0xd4a/0x2390 net/netfilter/ipvs/ip_vs_conn.c:1260
> Preemption disabled at:
> [<ffffffff898a6358>] bit_spin_lock include/linux/bit_spinlock.h:38 [inline]
> [<ffffffff898a6358>] hlist_bl_lock+0x18/0x110 include/linux/list_bl.h:149
> CPU: 0 UID: 0 PID: 16 Comm: ktimers/0 Tainted: G W L syzkaller #0 PREEMPT_{RT,(full)}
> Tainted: [W]=WARN, [L]=SOFTLOCKUP
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
> Call Trace:
> <TASK>
> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
> __might_resched+0x329/0x480 kernel/sched/core.c:9162
> __rt_spin_lock kernel/locking/spinlock_rt.c:48 [inline]
> rt_spin_lock+0xc2/0x400 kernel/locking/spinlock_rt.c:57
> spin_lock include/linux/spinlock_rt.h:45 [inline]
> ip_vs_conn_unlink net/netfilter/ipvs/ip_vs_conn.c:324 [inline]
> ip_vs_conn_expire+0xd4a/0x2390 net/netfilter/ipvs/ip_vs_conn.c:1260
> call_timer_fn+0x192/0x5e0 kernel/time/timer.c:1748
> expire_timers kernel/time/timer.c:1799 [inline]
> __run_timers kernel/time/timer.c:2374 [inline]
> __run_timer_base+0x6a3/0x9f0 kernel/time/timer.c:2386
> run_timer_base kernel/time/timer.c:2395 [inline]
> run_timer_softirq+0xb7/0x170 kernel/time/timer.c:2405
> handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622
> __do_softirq kernel/softirq.c:656 [inline]
> run_ktimerd+0x69/0x100 kernel/softirq.c:1151
> smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
> 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>
>