Subject: Re: [PATCH] net/sched: use spin_lock_bh() on &gact->tcf_lock

From: Simon Horman <[email-masked]>
Date: Sun, 1 Oct 2023 19:54:22 +0200

+  Pedro Tammela <[email-masked]>
   Po Liu <[email-masked]>

On Tue, Sep 26, 2023 at 06:26:25PM +0000, Chengfeng Ye wrote:
> I find tcf_gate_act() acquires &gact->tcf_lock without disable
> bh explicitly, as gact->tcf_lock is acquired inside timer under
> softirq context, if tcf_gate_act() is not called with bh disable
> by default or under softirq context(which I am not sure as I cannot
> find corresponding documentation), then it could be the following 
> deadlocks.
> 
> tcf_gate_act()
> --> spin_loc(&gact->tcf_lock)
> <interrupt>
>    --> gate_timer_func()
>    --> spin_lock(&gact->tcf_lock)
> 
> Signed-off-by: Chengfeng Ye <[email-masked]>

Hi Chengfeng Ye,

thanks for your patch.

As a fix for Networking this should probably be targeted at the
'net' tree. Which should be denoted in the subject.

        Subject: [PATCH net] ...

And as a fix this patch should probably have a Fixes tag.
This ones seem appropriate to me, but I could be wrong.

Fixes: a51c328df310 ("net: qos: introduce a gate control flow action")

I don't think it is necessary to repost just to address these issues,
but the Networking maintainers may think otherwise.

The code change itself looks good to me.

Reviewed-by: Simon Horman <[email-masked]>

> ---
>  net/sched/act_gate.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/net/sched/act_gate.c b/net/sched/act_gate.c
> index c9a811f4c7ee..b82daf7401a5 100644
> --- a/net/sched/act_gate.c
> +++ b/net/sched/act_gate.c
> @@ -124,25 +124,25 @@ TC_INDIRECT_SCOPE int tcf_gate_act(struct sk_buff *skb,
>  	tcf_lastuse_update(&gact->tcf_tm);
>  	tcf_action_update_bstats(&gact->common, skb);
>  
> -	spin_lock(&gact->tcf_lock);
> +	spin_lock_bh(&gact->tcf_lock);
>  	if (unlikely(gact->current_gate_status & GATE_ACT_PENDING)) {
> -		spin_unlock(&gact->tcf_lock);
> +		spin_unlock_bh(&gact->tcf_lock);
>  		return action;
>  	}
>  
>  	if (!(gact->current_gate_status & GATE_ACT_GATE_OPEN)) {
> -		spin_unlock(&gact->tcf_lock);
> +		spin_unlock_bh(&gact->tcf_lock);
>  		goto drop;
>  	}
>  
>  	if (gact->current_max_octets >= 0) {
>  		gact->current_entry_octets += qdisc_pkt_len(skb);
>  		if (gact->current_entry_octets > gact->current_max_octets) {
> -			spin_unlock(&gact->tcf_lock);
> +			spin_unlock_bh(&gact->tcf_lock);
>  			goto overlimit;
>  		}
>  	}
> -	spin_unlock(&gact->tcf_lock);
> +	spin_unlock_bh(&gact->tcf_lock);
>  
>  	return action;
>  
> -- 
> 2.17.1
> 
>