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

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Date: Sun, 28 Jan 2024 20:52:02 +0100
From: Stefan Wahren <wahrenst@....net>
To: Jakub Kicinski <kuba@...nel.org>
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

Hi Jakub,

Am 26.01.24 um 03:36 schrieb Jakub Kicinski:
> 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.
there is actually another reason for this change which is not mentioned
in the commit message. The pointer spi_thread can have 3 states:
- valid thread
- error pointer
- NULL

So the second motivation was to eliminate the possibility of an error
pointer
by using a local variable. So we only have to care about NULL.

I will change this in V4.
>
>> @@ -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.
Oops

Best regards
>
> Rest of the series LGTM!