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

From: Simon Horman
Date: Sun Oct 01 2023 - 13:54:31 EST


+ Pedro Tammela <pctammela@xxxxxxxxxxxx>
Po Liu <Po.Liu@xxxxxxx>

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 <dg573847474@xxxxxxxxx>


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 <horms@xxxxxxxxxx>

> ---
> 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
>
>