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Date:   Sat, 17 Sep 2022 10:05:24 -0700
From:   Jerry Snitselaar <jsnitsel@redhat.com>
To:     Dave Jiang <dave.jiang@intel.com>
Cc:     linux-kernel@vger.kernel.org, Fenghua Yu <fenghua.yu@intel.com>,
        Vinod Koul <vkoul@kernel.org>, dmaengine@vger.kernel.org
Subject: Re: [PATCH] dmaengine: idxd: Set workqueue state to disabled before
 trying to re-enable
Message-ID: <20220917170524.23wxvkhieroyrofd@cantor>
References: <20220824192913.2425634-1-jsnitsel@redhat.com>
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 <d0dbdd27-a890-1eea-63b5-ab6aaa27583e@intel.com>
 <f59ea139533f37991e786cd8cf4a0d591133d92c.camel@redhat.com>
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On Wed, Aug 24, 2022 at 03:19:51PM -0700, Dave Jiang wrote:
> 
> 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@intel.com>
> > > > > > Cc: Dave Jiang <dave.jiang@intel.com>
> > > > > > Cc: Vinod Koul <vkoul@kernel.org>
> > > > > > Cc: dmaengine@vger.kernel.org
> > > > > > Fixes: bfe1d56091c1 ("dmaengine: idxd: Init and probe for Intel
> > > > > > data accelerators")
> > > > > > Signed-off-by: Jerry Snitselaar <jsnitsel@redhat.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?
> 

Circling back to this. Since max_wqs could theoretically go up to 2^8, I guess
this would need to be done with the bitmap_* functions?

Regards,
Jerry

> 
> > 
> > > >  ????????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",