Re: [Intel-gfx] Major 2.6.38 / 2.6.39 / 3.0 regression ignored?

From: Kirill Smelkov
Date: Tue Aug 09 2011 - 12:33:32 EST

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In reply to: Vasily Khoruzhick: "Re: [Intel-gfx] Major 2.6.38 / 2.6.39 / 3.0 regression ignored?"
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On Tue, Aug 09, 2011 at 07:02:59PM +0300, Vasily Khoruzhick wrote:
> On Tuesday 09 August 2011 18:34:46 Kirill Smelkov wrote:
> > On Tue, Aug 09, 2011 at 06:09:57PM +0300, Vasily Khoruzhick wrote:
> > > On Tuesday 09 August 2011 17:47:56 Kirill Smelkov wrote:
> > > > On Tue, Aug 09, 2011 at 05:00:52PM +0300, Vasily Khoruzhick wrote:
> > > > > On Tuesday 09 August 2011 15:08:03 Kirill Smelkov wrote:
> > > > > > On Tue, Jul 26, 2011 at 05:48:27PM +0400, Kirill Smelkov wrote:
> > > > > > > On Sat, Jul 23, 2011 at 12:23:36AM +0400, Kirill Smelkov wrote:
> > > > > > > > Keith,
> > > > > > > >
> > > > > > > > first of all thanks for your prompt reply. Then...
> > > > > > > >
> > > > > > > > On Fri, Jul 22, 2011 at 11:00:41AM -0700, Keith Packard wrote:
> > > > > > > > > On Fri, 22 Jul 2011 15:08:06 +0400, Kirill Smelkov
> > > > > > > > > <kirr@xxxxxxxxxx>
> > > > >
> > > > > wrote:
> > > > > > > > > > And now after v3.0 is out, I've tested it again, and yes,
> > > > > > > > > > like it was broken on v3.0-rc5, it is (now even more)
> > > > > > > > > > broken on v3.0 -- after first
> > > > > > > > >
> > > > > > > > > > bad io access the system freezes completely:
> > > > > > > > > I looked at this when I first saw it (a couple of weeks ago),
> > > > > > > > > and I couldn't see any obvious reason this patch would cause
> > > > > > > > > this particular problem. I didn't want to revert the patch
> > > > > > > > > at that point as I feared it would cause other subtle
> > > > > > > > > problems. Given that you've got a work-around, it seemed
> > > > > > > > > best to just push this off past 3.0.
> > > > > > > >
> > > > > > > > What kind of a workaround are you talking about? Sorry, to me
> > > > > > > > it all looked like "UMS is being ignored forever". Anyway,
> > > > > > > > let's move on to try to solve the issue.
> > > > > > > >
> > > > > > > > > Given the failing address passed to ioread32, this seems like
> > > > > > > > > it's probably the call to READ_BREADCRUMB --
> > > > > > > > > I915_BREADCRUMB_INDEX is 0x21, which is an offset in 32-bit
> > > > > > > > > units within the hardware status page. If the
> > > > > > > > > status_page.page_addr value was zero, then the computed
> > > > > > > > > address would end up being 0x84.
> > > > > > > > >
> > > > > > > > > And, it looks like status_page.page_addr *will* end up being
> > > > > > > > > zero as a result of the patch in question. The patch resets
> > > > > > > > > the entire ring structure contents back to the initial
> > > > > > > > > values, which includes smashing the status_page structure to
> > > > > > > > > zero, clearing the value of status_page.page_addr set in
> > > > > > > > > i915_init_phys_hws.
> > > > > > > > >
> > > > > > > > > Here's an untested patch which moves the initialization of
> > > > > > > > > status_page.page_addr into intel_render_ring_init_dri. I note
> > > > > > > > > that intel_init_render_ring_buffer *already* has the setting
> > > > > > > > > of the status_page.page_addr value, and so I've removed the
> > > > > > > > > setting of status_page.page_addr from i915_init_phys_hws.
> > > > > > > > >
> > > > > > > > > I suspect we could remove the memset from
> > > > > > > > > intel_init_render_ring_buffer; it seems entirely superfluous
> > > > > > > > > given the memset in i915_init_phys_hws.
> > > > > > > > >
> > > > > > > > > From 159ba1dd207fc52590ce8a3afd83f40bd2cedf46 Mon Sep 17
> > > > > > > > > 00:00:00 2001 From: Keith Packard <keithp@xxxxxxxxxx>
> > > > > > > > > Date: Fri, 22 Jul 2011 10:44:39 -0700
> > > > > > > > > Subject: [PATCH] drm/i915: Initialize RCS ring status page
> > > > > > > > > address in
> > > > > > > > >
> > > > > > > > > intel_render_ring_init_dri
> > > > > > > > >
> > > > > > > > > Physically-addressed hardware status pages are initialized
> > > > > > > > > early in the driver load process by i915_init_phys_hws. For
> > > > > > > > > UMS environments, the ring structure is not initialized
> > > > > > > > > until the X server starts. At that point, the entire ring
> > > > > > > > > structure is re-initialized with all new values. Any values
> > > > > > > > > set in the ring structure (including
> > > > > > > > > ring->status_page.page_addr) will be lost when the ring is
> > > > > > > > > re-initialized.
> > > > > > > > >
> > > > > > > > > This patch moves the initialization of the
> > > > > > > > > status_page.page_addr value to intel_render_ring_init_dri.
> > > > > > > > >
> > > > > > > > > Signed-off-by: Keith Packard <keithp@xxxxxxxxxx>
> > > > > > > > > ---
> > > > > > > > >
> > > > > > > > > drivers/gpu/drm/i915/i915_dma.c | 6 ++----
> > > > > > > > > drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
> > > > > > > > > 2 files changed, 5 insertions(+), 4 deletions(-)
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > > b/drivers/gpu/drm/i915/i915_dma.c index 1271282..8a3942c
> > > > > > > > > 100644 --- a/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > > +++ b/drivers/gpu/drm/i915/i915_dma.c
> > > > > > > > > @@ -61,7 +61,6 @@ static void i915_write_hws_pga(struct
> > > > > > > > > drm_device *dev)
> > > > > > > > >
> > > > > > > > > static int i915_init_phys_hws(struct drm_device *dev)
> > > > > > > > > {
> > > > > > > > >
> > > > > > > > > drm_i915_private_t *dev_priv = dev->dev_private;
> > > > > > > > >
> > > > > > > > > - struct intel_ring_buffer *ring = LP_RING(dev_priv);
> > > > > > > > >
> > > > > > > > > /* Program Hardware Status Page */
> > > > > > > > > dev_priv->status_page_dmah =
> > > > > > > > >
> > > > > > > > > @@ -71,10 +70,9 @@ static int i915_init_phys_hws(struct
> > > > > > > > > drm_device *dev)
> > > > > > > > >
> > > > > > > > > DRM_ERROR("Can not allocate hardware status page\n");
> > > > > > > > > return -ENOMEM;
> > > > > > > > >
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > - ring->status_page.page_addr =
> > > > > > > > > - (void __force __iomem *)dev_priv->status_page_dmah-
> >vaddr;
> > > > > > > > >
> > > > > > > > > - memset_io(ring->status_page.page_addr, 0, PAGE_SIZE);
> > > > > > > > > + memset_io((void __force __iomem
> > > > > > > > > *)dev_priv->status_page_dmah->vaddr, + 0, PAGE_SIZE);
> > > > > > > > >
> > > > > > > > > i915_write_hws_pga(dev);
> > > > > > > > >
> > > > > > > > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > > b/drivers/gpu/drm/i915/intel_ringbuffer.c index
> > > > > > > > > e961568..47b9b27 100644
> > > > > > > > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > > @@ -1321,6 +1321,9 @@ int intel_render_ring_init_dri(struct
> > > > > > > > > drm_device *dev, u64 start, u32 size)
> > > > > > > > >
> > > > > > > > > ring->get_seqno = pc_render_get_seqno;
> > > > > > > > >
> > > > > > > > > }
> > > > > > > > >
> > > > > > > > > + if (!I915_NEED_GFX_HWS(dev))
> > > > > > > > > + ring->status_page.page_addr =
> > > > > > > > > dev_priv->status_page_dmah->vaddr; +
> > > > > > > > >
> > > > > > > > > ring->dev = dev;
> > > > > > > > > INIT_LIST_HEAD(&ring->active_list);
> > > > > > > > > INIT_LIST_HEAD(&ring->request_list);
> > > > > > > >
> > > > > > > > I can't tell whether this is correct, because intel gfx driver
> > > > > > > > is unknown to me, but from the first glance your description
> > > > > > > > sounds reasonable.
> > > > > > > >
> > > > > > > > I'm out of office till ~ next week's tuesday, and on return
> > > > > > > > I'll try to test it on the hardware in question.
> > > > > > >
> > > > > > > Keith, thanks again for the patch. As promised I've tested it on
> > > > > > > the hardware in question and yes, bad_access is gone and X seems
> > > > > > > to work, so thank you, but...
> > > > > > >
> > > > > > >
> > > > > > > I see there are more such bugs in introduced-in-guilty-patch
> > > > > > > intel_render_ring_init_dri(). For example ring->irq_queue is
> > > > > > > left uninitialized and also ring->irq_lock etc...
> > > > > > >
> > > > > > >
> > > > > > > I'm X newbie, so if here is something stupid X-wise, please don't
> > > > > > > beat me too hard, but to me the gist of the problem is the
> > > > > > > original patch, where Chris does
> > > > > > >
> > > > > > > ( git show e8616b6ced6137085e6657cc63bc2fe3900b8616 )
> > > > > > >
> > > > > > > > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > b/drivers/gpu/drm/i915/intel_ringbuffer.c index
> > > > > > > > 03e3370..51fbc5e 100644
> > > > > > > > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > > > > > > > @@ -1291,6 +1291,48 @@ int intel_init_render_ring_buffer(struct
> > > > > > > > drm_device *dev)
> > > > > > > >
> > > > > > > > return intel_init_ring_buffer(dev, ring);
> > > > > > > >
> > > > > > > > }
> > > > > > > >
> > > > > > > > +int intel_render_ring_init_dri(struct drm_device *dev, u64
> > > > > > > > start, u32 size) +{
> > > > > > > > + drm_i915_private_t *dev_priv = dev->dev_private;
> > > > > > > > + struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> > > > > > > > +
> > > > > > > > + *ring = render_ring;
> > > > > > > >
> > > > > > > ^^^^^^^^^^^^^^^^^^^
> > > > > > > here resets
> > > > > > > >
> > > > > > > > + if (INTEL_INFO(dev)->gen >= 6) {
> > > > > > > > + ring->add_request = gen6_add_request;
> > > > > > > > + ring->irq_get = gen6_render_ring_get_irq;
> > > > > > > > + ring->irq_put = gen6_render_ring_put_irq;
> > > > > > > > + } else if (IS_GEN5(dev)) {
> > > > > > > > + ring->add_request = pc_render_add_request;
> > > > > > > > + ring->get_seqno = pc_render_get_seqno;
> > > > > > > > + }
> > > > > > >
> > > > > > > and then the rest of the `ring` is initialized seemingly
> > > > > > > copy-pasted
> > > > > > >
> > > > > > > from intel_init_ring_buffer():
> > > > > > > > + ring->dev = dev;
> > > > > > > > + INIT_LIST_HEAD(&ring->active_list);
> > > > > > > > + INIT_LIST_HEAD(&ring->request_list);
> > > > > > > > + INIT_LIST_HEAD(&ring->gpu_write_list);
> > > > > > > > +
> > > > > > > > + ring->size = size;
> > > > > > > > + ring->effective_size = ring->size;
> > > > > > > > + if (IS_I830(ring->dev))
> > > > > > > > + ring->effective_size -= 128;
> > > > > > > > +
> > > > > > > > + ring->map.offset = start;
> > > > > > > > + ring->map.size = size;
> > > > > > > > + ring->map.type = 0;
> > > > > > > > + ring->map.flags = 0;
> > > > > > > > + ring->map.mtrr = 0;
> > > > > > >
> > > > > > > ...
> > > > > > >
> > > > > > > where both 3 chunks go almost exactly from
> > > > > > > intel_init_ring_buffer(), and ring->effective_size tweak even
> > > > > > > stripped original comment:
> > > > > > >
> > > > > > > # original version from intel_init_ring_buffer():
> > > > > > > /* Workaround an erratum on the i830 which causes a hang
> > > > > > > if
> > > > > > >
> > > > > > > * the TAIL pointer points to within the last 2
> > > > > > > cachelines * of the buffer.
> > > > > > > */
> > > > > > >
> > > > > > > ring->effective_size = ring->size;
> > > > > > > if (IS_I830(ring->dev))
> > > > > > >
> > > > > > > ring->effective_size -= 128;
> > > > > > >
> > > > > > > ...
> > > > > > >
> > > > > > >
> > > > > > > The line marked "here resets" resets all the fields, and maybe
> > > > > > > it's not a good idea to re-initialize them all afterwards
> > > > > > > (missing some as this thread show), or at least if it is really
> > > > > > > needed, share initialization code between
> > > > > > > intel_render_ring_init_dri() and intel_init_ring_buffer() ?
> > > > > > >
> > > > > > > >From the outside it looks like the offending patch was done as a
> > > > > > > >quick
> > > > > > >
> > > > > > > fix in a hurry (lots of copy-paste), and maybe it would be better
> > > > > > > to re-do it properly...
> > > > > >
> > > > > > Silence... ?
> > > > > >
> > > > > > I read UMS is still ignored, because e.g. that uninitialized
> > > > > > ring->irq_lock which I've wrote about above is for sure used e.g.
> > > > > > in gen6_render_ring_get_irq() added to ring vtable in
> > > > > > intel_render_ring_init_dri().
> > > > >
> > > > > I really doubt that UMS supports gen6 hardware.
> > > >
> > > > Then why it is there in intel_render_ring_init_dri():
> > > > int intel_render_ring_init_dri(struct drm_device *dev, u64 start,
> > > > u32
> > > >
> > > > size) {
> > > >
> > > > drm_i915_private_t *dev_priv = dev->dev_private;
> > > > struct intel_ring_buffer *ring = &dev_priv->ring[RCS];
> > > >
> > > > *ring = render_ring;
> > > > if (INTEL_INFO(dev)->gen >= 6) {
> > >
> > > This branch executes only when hw generation is 6 or newer.
> >
> > and adds gen6_render_ring_get_irq() to vtable which uses ring->irq_lock
> > which is left uninitialized.
> >
> > I don't understand what you were trying to say. How does it matter if
> > some branch executes only for such-and-such hardware, when this branch
> > contains bugs? Could you please clarify?
>
> I want to say that xf86-video-intel with gen6 support does not support UMS. So
> you can't even hit this "bug".

Ok, but so then there is a dead code in the kernel, right? Or not dead
at all because potentially some non-X userspace could trigger the bug.

Why it was added in the first place?

To me, intel_render_ring_init_dri() looks like being copy-pasted from
several places in a hurry. And I was already beaten by one bug
introduced in it, without a single response for 3 kernel cycles though
I've asked for help several times and provided detailed info.

Finally Keith analyzed and plugged NULL-pointer dereference (thanks)
but I'm telling, it seems there are more bugs introduced in e8616b6c.

The patch title says "drm/i915: Initialise ring vfuncs for old DRI
paths" and one could ask, why couldn't it be done without bugs and
regressions. Are we waiting for another one hitting left bugs instead of
fix them in the first place?

Quite frankly, I don't understand intel-gfx developers attitude: why is
it me, just random user who is nitpicking here? Why there is no
interest/will to analyze now obviously buggy/duplicate code and fix it?

If support for UMS/old-dri/whatever is dropped, could you please say so
and clean the driver from legacy code and move on. That would be at
least fair for people not hoping their old setups will continue to
work.

Thanks,
Kirill
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Next message: Paul Parsons: "[PATCH] mfd: asic3: Fix SD card resume after suspend"
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In reply to: Vasily Khoruzhick: "Re: [Intel-gfx] Major 2.6.38 / 2.6.39 / 3.0 regression ignored?"
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