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:

quoted

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@gmx.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