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

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Date:   Thu, 23 Nov 2023 12:26:53 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Stefan Wahren <wahrenst@....net>,
        "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

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.

Additionally I think you can drop the 'if (qca->spi_thread)' in
qcaspi_intr_handler()

Cheers,

Paolo