Hi Jakub,

Am 26.01.24 um 03:36 schrieb Jakub Kicinski:

On Wed, 24 Jan 2024 23:31:58 +0100 Stefan Wahren wrote:

quoted

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.

quoted

@@ -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!