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Date: Wed, 24 Aug 2022 15:19:51 -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 3:07 PM, Jerry Snitselaar wrote:
> On Wed, 2022-08-24 at 14:59 -0700, Dave Jiang wrote:
>> 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?
>>
> Ah, yeah I see that now. So, if it does set the state to disabled in
> idxd_wq_disable_cleanup(), does it have another means to track which
> wqs need to be re-enabled for that loop that happens after the
> idxd_device_reset() call?
Oh I see what you mean... So we can either do what you did or create a
mask and mark the WQ that are "enabled" before reset. Maybe that's
cleaner rather than relying on the side effect of the WQ state isn't
cleared? Thoughts?
>
>>> 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",
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