linux-kernel - Re: [PATCH 1/4 net] qca_spi: Fix SPI thread creation

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Message-ID: <d4385cad-41e2-4adc-99b1-45a5b75a2ad5@gmx.net>
Date:   Fri, 24 Nov 2023 14:40:33 +0100
From:   Stefan Wahren <wahrenst@....net>
To:     Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4 net] qca_spi: Fix SPI thread creation

Hi Paolo,

Am 23.11.23 um 12:26 schrieb Paolo Abeni:
> On Tue, 2023-11-21 at 17:30 +0100, Stefan Wahren wrote:
>> The qca_spi driver create/stop the SPI kernel thread in case
>> of netdev_open/close. This is a big issue because it allows
>> userspace to prevent from restarting the SPI thread after
>> ring parameter changes (e.g. signals which stop the thread).
>> This could be done by terminating a script which changes
>> the ring parameter in a loop.
>>
>> So fix this by moving create/stop of the SPI kernel into
>> the init/uninit ops. The open/close ops could be realized just
>> by 'park/unpark' the SPI kernel thread.
>>
>> Fixes: 291ab06ecf67 ("net: qualcomm: new Ethernet over SPI driver for QCA7000")
>> Signed-off-by: Stefan Wahren <wahrenst@....net>
>> ---
>>   drivers/net/ethernet/qualcomm/qca_spi.c | 35 ++++++++++++++++---------
>>   1 file changed, 23 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/qualcomm/qca_spi.c b/drivers/net/ethernet/qualcomm/qca_spi.c
>> index bec723028e96..b11a998b2456 100644
>> --- a/drivers/net/ethernet/qualcomm/qca_spi.c
>> +++ b/drivers/net/ethernet/qualcomm/qca_spi.c
>> @@ -580,6 +580,11 @@ qcaspi_spi_thread(void *data)
>>   	netdev_info(qca->net_dev, "SPI thread created\n");
>>   	while (!kthread_should_stop()) {
>>   		set_current_state(TASK_INTERRUPTIBLE);
>> +		if (kthread_should_park()) {
>> +			kthread_parkme();
>> +			continue;
>> +		}
>> +
>>   		if ((qca->intr_req == qca->intr_svc) &&
>>   		    !qca->txr.skb[qca->txr.head])
>>   			schedule();
>> @@ -679,25 +684,17 @@ qcaspi_netdev_open(struct net_device *dev)
>>   	qca->sync = QCASPI_SYNC_UNKNOWN;
>>   	qcafrm_fsm_init_spi(&qca->frm_handle);
>>
>> -	qca->spi_thread = kthread_run((void *)qcaspi_spi_thread,
>> -				      qca, "%s", dev->name);
>> -
>> -	if (IS_ERR(qca->spi_thread)) {
>> -		netdev_err(dev, "%s: unable to start kernel thread.\n",
>> -			   QCASPI_DRV_NAME);
>> -		return PTR_ERR(qca->spi_thread);
>> -	}
>> -
>>   	ret = request_irq(qca->spi_dev->irq, qcaspi_intr_handler, 0,
>>   			  dev->name, qca);
>>   	if (ret) {
>>   		netdev_err(dev, "%s: unable to get IRQ %d (irqval=%d).\n",
>>   			   QCASPI_DRV_NAME, qca->spi_dev->irq, ret);
>> -		kthread_stop(qca->spi_thread);
>>   		return ret;
>>   	}
>>
>>   	/* SPI thread takes care of TX queue */
>> +	kthread_unpark(qca->spi_thread);
>> +	wake_up_process(qca->spi_thread);
> The above looks racy: after 'request_irq()' the interrupt handler can
> raise an irq before the thread being unparked.
yes fixing the whole resource allocation issue requires patch 1 and 2
applied, which should avoid the race. But i didn't want to combine both
patches to keep it applicable for stable. My thought was that 2 smaller
patches are more acceptable than a big one.

Should i squash them?

My concern is about the amount of affected devices. The QCA7000 is used
mostly in EV charging stations and EVs. I don't how many of them use
this driver.

> Additionally I think you can drop the 'if (qca->spi_thread)' in
> qcaspi_intr_handler()
Thanks i will check that for the next version.
>
> Cheers,
>
> Paolo
>