Re: [PATCH] [v2] net: sched: gred: dynamically allocate tc_gred_qopt_offload

From: Jakub Kicinski
Date: Tue Oct 19 2021 - 18:08:59 EST


On Tue, 19 Oct 2021 21:15:29 +0200 Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> The tc_gred_qopt_offload structure has grown too big to be on the
> stack for 32-bit architectures after recent changes.
>
> net/sched/sch_gred.c:903:13: error: stack frame size (1180) exceeds limit (1024) in 'gred_destroy' [-Werror,-Wframe-larger-than]
> net/sched/sch_gred.c:310:13: error: stack frame size (1212) exceeds limit (1024) in 'gred_offload' [-Werror,-Wframe-larger-than]
>
> Use dynamic allocation per qdisc to avoid this.
>
> Fixes: 50dc9a8572aa ("net: sched: Merge Qdisc::bstats and Qdisc::cpu_bstats data types")
> Fixes: 67c9e6270f30 ("net: sched: Protect Qdisc::bstats with u64_stats")
> Suggested-by: Jakub Kicinski <kuba@xxxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> Hi Jakub,
>
> Not sure if this is what you had in mind, if not it might be easier
> if you do it yourself. In particular, adding tc_gred_qopt_offload
> to gred_sched directly rather than as a pointer may be easier here,
> but that may have other downsides.

This is exactly what I had in mind, thanks!

Two minor nits if you're willing to respin, if you feel like you've
spent enough time on this already we can marge as is :)

> - opt.set.qstats = &sch->qstats;
> + opt->set.qstats = &sch->qstats;
> }
>
> - dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_GRED, &opt);
> + dev->netdev_ops->ndo_setup_tc(dev, TC_SETUP_QDISC_GRED, opt);
> +
> + return;

return no longer needed

> }
>
> static int gred_offload_dump_stats(struct Qdisc *sch)

> @@ -754,6 +759,10 @@ static int gred_init(struct Qdisc *sch, struct nlattr *opt,
> sch->limit = qdisc_dev(sch)->tx_queue_len
> * psched_mtu(qdisc_dev(sch));

The ops should not change, so I think we can do

if (qdisc_dev(sch)->netdev_ops->ndo_setup_tc) {

> + table->opt = kzalloc(sizeof(table->opt), GFP_KERNEL);
> + if (!table->opt)
> + return -ENOMEM;
> +
> return gred_change_table_def(sch, tb[TCA_GRED_DPS], extack);
> }
>