On 08.12.2025 15:06, Rukomoinikova Aleksandra wrote:
> Hi!
> I was testing conntrack limiting using Open vSwitch and noticed the
> following issue: under certain limits, a CPU lock occurred.
>
> [ 491.682936] watchdog: BUG: soft lockup - CPU#1 stuck for 26s! [ovs-
> dpctl:19437]
>
> This occurs during a high packet frequency when trying to get the set
> limits through ovs-dpctl ct-get-limits.
>
> In the trace, I can see that the lock occurred on attempts to acquire a
> spinlock.
>
> [ 491.683056] <IRQ>
> [ 491.683059] _raw_spin_lock_bh+0x29/0x30
> [ 491.683064] count_tree+0x19b/0x1f0 [nf_conncount]
> [ 491.683069] ovs_ct_commit+0x196/0x490 [openvswitch]
>
> Prior to this, in the trace, there was processing of a task from
> userspace (ovs-dpctl)
>
> [ 491.683236] </IRQ>
> [ 491.683237] <TASK>
> [ 491.683238] asm_common_interrupt+0x22/0x40
> [ 491.683240] RIP: 0010:nf_conncount_gc_list+0x18a/0x200 [nf_conncount]
>
> Inside the nf_conncount_gc_list function, a lock is taken on
> nf_conncount.c:spin_trylock_bh(&list->list_lock):335. After this, the
> not-so-fast __nf_conncount_gc_list function is executed. If, at this
> moment, a packet interrupt arrives on the same сpu core (and
> spin_trylock_bh doesn't disable interrupts on that core), then scenario
> I encountered occurs: the first lock remains held, while the packet
> interrupt also attempts to acquire it at
> nf_conncount.c:spin_lock_bh(&rbconn->list.list_lock):502 while
> committing to conntrack. This attempt fails, leading to a soft lockup.
>
> Hence my question: shouldn't we avoid calling nf_conncount_gc_list when
> querying limits without an skb (as OVS does in openvswitch/
> conntrack.c:1773)? The limit retrieval operation should be read-only
> regarding the contract state, not involve potential modification.
>
> Like this:
> --- a/net/netfilter/nf_conncount.c
> +++ b/net/netfilter/nf_conncount.c
> @@ -495,7 +495,6 @@ count_tree(struct net *net,
> int ret;
>
> if (!skb) {
> - nf_conncount_gc_list(net, &rbconn->list);
> return rbconn->list.count;
> }
>
> Thanks!
>
> --
> regards,
> Alexandra.
>
+ ovs-dev ML
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