Re: [PATCH net-next v4 2/6] net: ti: icssg-stats: Move long delayed work on system_dfl_long_wq

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- [Medium] The conversion is incomplete, so one delayed_work is queued on
  two different workqueues.

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net: ti: icssg-stats: Move long delayed work on system_dfl_long_wq

This commit changes the self-requeue in icssg_stats_work_handler() from
the per-cpu system_long_wq to the unbound system_dfl_long_wq. The goal is
to let the periodic stats work benefit from scheduler task placement.

> diff --git a/drivers/net/ethernet/ti/icssg/icssg_stats.c b/drivers/net/ethernet/ti/icssg/icssg_stats.c
> index 7159baa0155cf..7d6d6692d8192 100644
> --- a/drivers/net/ethernet/ti/icssg/icssg_stats.c
> +++ b/drivers/net/ethernet/ti/icssg/icssg_stats.c
> @@ -69,7 +69,7 @@ void icssg_stats_work_handler(struct work_struct *work)
>  						stats_work.work);
>  	emac_update_hardware_stats(emac);
>  
> -	queue_delayed_work(system_long_wq, &emac->stats_work,
> +	queue_delayed_work(system_dfl_long_wq, &emac->stats_work,
>  			   msecs_to_jiffies((STATS_TIME_LIMIT_1G_MS * 1000) / emac->speed));
>  }

[Severity: Medium]
Is this conversion complete?

Both ICSSG drivers use icssg_stats_work_handler() for the same
emac->stats_work. Both prueth_netdev_init() functions, in icssg_prueth.c
and icssg_prueth_sr1.c, do this:

    INIT_DELAYED_WORK(&emac->stats_work, icssg_stats_work_handler);

However, the first run is still queued on the per-cpu workqueue from
the ndo_open path:

drivers/net/ethernet/ti/icssg/icssg_prueth_sr1.c:emac_ndo_open() {
    ...
	queue_work(system_long_wq, &emac->stats_work.work);
    ...
}

The follow-up patch "net: ti: icssg-prueth: Move long delayed work on
system_dfl_long_wq" converts the matching call in icssg_prueth.c. No
patch in the series seems to change icssg_prueth_sr1.c.

On SR1.0 hardware, the first stats run after each open would still go to
a per-cpu worker. Every later run would go to system_dfl_long_wq.

Could mixing the two workqueues also bypass the non-reentrancy check in
__queue_work()?

kernel/workqueue.c:__queue_work() {
    ...
		if (worker && worker->current_pwq->wq == wq) {
    ...
}

The instance running on system_long_wq re-arms onto system_dfl_long_wq,
so this check fails. If the timer expires before the first worker
returns, a second instance could start at the same time on another
worker.

Today this looks harmless. The handler does nothing after
queue_delayed_work(), and emac_update_hardware_stats() takes
prueth->stats_lock.

Should emac_ndo_open() in icssg_prueth_sr1.c also switch to
system_dfl_long_wq, so stats_work is only ever queued on one workqueue?

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Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261012095452.135828-1-marco.crivellari%40suse.com