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 14:59:29 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Jerry Snitselaar <jsnitsel@...hat.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 8/24/2022 2:16 PM, Jerry Snitselaar wrote:
> 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:

idxd_device_reinit() should called idxd_device_reset() first. And that 
should at some point call idxd_wq_disable_cleanup() and clean up the states.

https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/dma/idxd/irq.c#L42

https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/dma/idxd/device.c#L725

https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/dma/idxd/device.c#L711

https://elixir.bootlin.com/linux/v6.0-rc2/source/drivers/dma/idxd/device.c#L376

So if we stick the wq state reset in there, it should show up as 
"disabled" by the time we try to enable the WQs again. Does that look 
reasonable?


>
> 	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",