linux-kernel - Re: [PATCH] dmaengine: idxd: Set workqueue state to disabled before trying to re-enable

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Date:   Wed, 24 Aug 2022 14:16:25 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Dave Jiang <dave.jiang@...el.com>
Cc:     linux-kernel@...r.kernel.org, Fenghua Yu <fenghua.yu@...el.com>,
        Vinod Koul <vkoul@...nel.org>, dmaengine@...r.kernel.org
Subject: Re: [PATCH] dmaengine: idxd: Set workqueue state to disabled before
 trying to re-enable

On Wed, Aug 24, 2022 at 01:29:03PM -0700, Dave Jiang wrote:
> 
> On 8/24/2022 12:29 PM, Jerry Snitselaar wrote:
> > For a software reset idxd_device_reinit() is called, which will walk
> > the device workqueues to see which ones were enabled, and try to
> > re-enable them. It keys off wq->state being iDXD_WQ_ENABLED, but the
> > first thing idxd_enable_wq() will do is see that the state of the
> > workqueue is enabled, and return 0 instead of attempting to issue
> > a command to enable the workqueue.
> > 
> > So once a workqueue is found that needs to be re-enabled,
> > set the state to disabled prior to calling idxd_enable_wq().
> > This would accurately reflect the state if the enable fails
> > as well.
> > 
> > Cc: Fenghua Yu <fenghua.yu@...el.com>
> > Cc: Dave Jiang <dave.jiang@...el.com>
> > Cc: Vinod Koul <vkoul@...nel.org>
> > Cc: dmaengine@...r.kernel.org
> > Fixes: bfe1d56091c1 ("dmaengine: idxd: Init and probe for Intel data accelerators")
> > Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>
> > ---
> >   drivers/dma/idxd/irq.c | 1 +
> >   1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/dma/idxd/irq.c b/drivers/dma/idxd/irq.c
> > index 743ead5ebc57..723eeb5328d6 100644
> > --- a/drivers/dma/idxd/irq.c
> > +++ b/drivers/dma/idxd/irq.c
> > @@ -52,6 +52,7 @@ static void idxd_device_reinit(struct work_struct *work)
> >   		struct idxd_wq *wq = idxd->wqs[i];
> >   		if (wq->state == IDXD_WQ_ENABLED) {
> > +			wq->state = IDXD_WQ_DISABLED;
> Might be better off to insert this line in idxd_wq_disable_cleanup(). I
> think that should put it in sane state.

I don't think that is called in the code path that I was lookng at. I've been
looking at this bit of process_misc_interrupts():

halt:
	gensts.bits = ioread32(idxd->reg_base + IDXD_GENSTATS_OFFSET);
	if (gensts.state == IDXD_DEVICE_STATE_HALT) {
		idxd->state = IDXD_DEV_HALTED;
		if (gensts.reset_type == IDXD_DEVICE_RESET_SOFTWARE) {
			/*
			 * If we need a software reset, we will throw the work
			 * on a system workqueue in order to allow interrupts
			 * for the device command completions.
			 */
			INIT_WORK(&idxd->work, idxd_device_reinit);
			queue_work(idxd->wq, &idxd->work);
		} else {
			idxd->state = IDXD_DEV_HALTED;
			idxd_wqs_quiesce(idxd);
			idxd_wqs_unmap_portal(idxd);
			spin_lock(&idxd->dev_lock);
			idxd_device_clear_state(idxd);
			dev_err(&idxd->pdev->dev,
				"idxd halted, need %s.\n",
				gensts.reset_type == IDXD_DEVICE_RESET_FLR ?
				"FLR" : "system reset");
			spin_unlock(&idxd->dev_lock);
			return -ENXIO;
		}
	}

	return 0;
}

So it sees that the device is halted, and sticks idxd_device_reinint() on that
workqueue. The idxd_device_reinit() has this loop to re-enable the idxd wqs:

	for (i = 0; i < idxd->max_wqs; i++) {
		struct idxd_wq *wq = idxd->wqs[i];

		if (wq->state == IDXD_WQ_ENABLED) {
			wq->state = IDXD_WQ_DISABLED;
			rc = idxd_wq_enable(wq);
			if (rc < 0) {
				dev_warn(dev, "Unable to re-enable wq %s\n",
					 dev_name(wq_confdev(wq)));
			}
		}
	}

Once you go into idxd_wq_enable() though you get this check at the beginning:

 	if (wq->state == IDXD_WQ_ENABLED) {
		dev_dbg(dev, "WQ %d already enabled\n", wq->id);
		return 0;
	}

So IIUC it sees the device is halted, goes to reset it, figures out a wq
should be re-enabled, calls idxd_wq_enable() which hits the check, returns
0 and the wq is never really re-enabled, though it will still have wq state
set to IDXD_WQ_ENABLED.

Or am I missing something?

Regards,
Jerry

> >   			rc = idxd_wq_enable(wq);
> >   			if (rc < 0) {
> >   				dev_warn(dev, "Unable to re-enable wq %s\n",