linux-kernel - Re: [PATCH V3 01/14 next] qca_spi: Improve SPI thread creation

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Date: Thu, 25 Jan 2024 18:36:39 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Stefan Wahren <wahrenst@....net>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Lino Sanfilippo
 <LinoSanfilippo@....de>, Florian Fainelli <f.fainelli@...il.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 01/14 next] qca_spi: Improve SPI thread creation

On Wed, 24 Jan 2024 23:31:58 +0100 Stefan Wahren wrote:
> The qca_spi driver create/stop the SPI kernel thread in case
> of netdev_open/close. This isn't optimal because there is no
> need for such an expensive operation.
> 
> So improve this by moving create/stop of the SPI kernel into
> the init/uninit ops. The open/close ops could just
> 'park/unpark' the SPI kernel thread.

What's the concern? I don't think that creating a thread is all
expensive. And we shouldn't have a thread sitting around when
the interface isn't use. I mean - if you ask me what's better
a small chance that the creation will fail at open or having
a parked and unused thread when device is down - I'd pick
the former.. But I may well be missing the point.

> @@ -825,6 +813,7 @@ static int
>  qcaspi_netdev_init(struct net_device *dev)
>  {
>  	struct qcaspi *qca = netdev_priv(dev);
> +	struct task_struct *thread;
> 
>  	dev->mtu = QCAFRM_MAX_MTU;
>  	dev->type = ARPHRD_ETHER;
> @@ -848,6 +837,15 @@ qcaspi_netdev_init(struct net_device *dev)
>  		return -ENOBUFS;
>  	}
> 
> +	thread = kthread_create(qcaspi_spi_thread, qca, "%s", dev->name);
> +	if (IS_ERR(thread)) {
> +		netdev_err(dev, "%s: unable to start kernel thread.\n",
> +			   QCASPI_DRV_NAME);
> +		return PTR_ERR(thread);

I'm 90% sure this leaks resources on failure, too.

Rest of the series LGTM!