On 4/17/25 11:08 AM, Sebastian Andrzej Siewior wrote:
> On 2025-04-17 10:01:17 [+0200], Paolo Abeni wrote:
>> @Sebastian: I think the 'owner' assignment could be optimized out at
>> compile time for non RT build - will likely not matter for performances,
>> but I think it will be 'nicer', could you please update the patches to
>> do that?
>
> If we don't assign the `owner' then we can't use the lock even on !RT
> because lockdep should complain. What about this then:
>
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index a3989d450a67f..b8f766978466d 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -294,8 +294,11 @@ void ovs_dp_process_packet(struct sk_buff *skb, struct
> sw_flow_key *key)
> sf_acts = rcu_dereference(flow->sf_acts);
> /* This path can be invoked recursively: Use the current task to
> * identify recursive invocation - the lock must be acquired only once.
> + * Even with disabled bottom halves this can be preempted on PREEMPT_RT.
> + * Limit the provecc to RT to avoid assigning `owner' if it can be
> + * avoided.
> */
> - if (ovs_pcpu->owner != current) {
> + if (IS_ENABLED(CONFIG_PREEMPT_RT) && ovs_pcpu->owner != current) {
> local_lock_nested_bh(&ovs_pcpu_storage.bh_lock);
> ovs_pcpu->owner = current;
> ovs_pcpu_locked = true;
> @@ -687,9 +690,11 @@ static int ovs_packet_cmd_execute(struct sk_buff *skb,
> struct genl_info *info)
>
> local_bh_disable();
> local_lock_nested_bh(&ovs_pcpu_storage.bh_lock);
> - this_cpu_write(ovs_pcpu_storage.owner, current);
> + if (IS_ENABLED(CONFIG_PREEMPT_RT))
> + this_cpu_write(ovs_pcpu_storage.owner, current);
Perhaps implement the above 2 lines in an helper, to keep the code tidy?
otherwise LGTM.
Thanks,
Paolo
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