3.18-rc regression: drm/nouveau: use shared fences for readable objects

[Michael Marineau]

On Nov 20, 2014 12:53 AM, "Maarten Lankhorst" <
maarten.lankhorst at canonical.com> wrote:
>
> Op 20-11-14 om 05:06 schreef Michael Marineau:
> > On Wed, Nov 19, 2014 at 12:10 AM, Maarten Lankhorst
> > <maarten.lankhorst at canonical.com> wrote:
> >> Hey,
> >>
> >> On 19-11-14 07:43, Michael Marineau wrote:
> >>> On 3.18-rc kernel's I have been intermittently experiencing GPU
> >>> lockups shortly after startup, accompanied with one or both of the
> >>> following errors:
> >>>
> >>> nouveau E[   PFIFO][0000:01:00.0] read fault at 0x000734a000 [PTE]
> >>> from PBDMA0/HOST_CPU on channel 0x007faa3000 [unknown]
> >>> nouveau E[     DRM] GPU lockup - switching to software fbcon
> >>>
> >>> I was able to trace the issue with bisect to commit
> >>> 809e9447b92ffe1346b2d6ec390e212d5307f61c "drm/nouveau: use shared
> >>> fences for readable objects". The lockups appear to have cleared up
> >>> since reverting that and a few related followup commits:
> >>>
> >>> 809e9447: "drm/nouveau: use shared fences for readable objects"
> >>> 055dffdf: "drm/nouveau: bump driver patchlevel to 1.2.1"
> >>> e3be4c23: "drm/nouveau: specify if interruptible wait is desired in
> >>> nouveau_fence_sync"
> >>> 15a996bb: "drm/nouveau: assign fence_chan->name correctly"
> >> Weird. I'm not sure yet what causes it.
> >>
> >>
http://cgit.freedesktop.org/~mlankhorst/linux/commit/?h=fixed-fences-for-bisect&id=86be4f216bbb9ea3339843a5658d4c21162c7ee2
> > Building a kernel from that commit gives me an entirely new behavior:
> > X hangs for at least 10-20 seconds at a time with brief moments of
> > responsiveness before hanging again while gitk on the kernel repo
> > loads. Otherwise the system is responsive. The head of that
> > fixed-fences-for-bisect branch (1c6aafb5) which is the "use shared
> > fences for readable objects" commit I originally bisected to does
> > feature the complete lockups I was seeing before.
> Ok for the sake of argument lets just assume they're separate bugs, and
we should look at xorg
> hanging first.
>
> Is there anything in the dmesg when the hanging happens?

Nothing in dmesg, I will try some more experiments shortly including the
ones you suggest below. Just in case it wasn't clear those xorg hangs do
not happen on the branch head if I get lucky and manage to log in without
the GPU lockup so if they are different bugs it at least appears that both
present at the same time.

>
> And it's probably 15 seconds, if it's called through nouveau_fence_wait.
>
> Try changing else if (!ret) to else if (WARN_ON(!ret)) in that function,
and see if you get some dmesg spam. :)
>
>
> >> On the EDITED patch from fixed-fences-for-bisect, can you do the
following:
> >>
> >> In nouveau/nv84_fence.c function nv84_fence_context_new, remove
> >>
> >> fctx->base.sequence = nv84_fence_read(chan);
> >>
> >> and add back
> >>
> >> nouveau_bo_wr32(priv->bo, chan->chid * 16/4, 0x00000000);
> > Making your suggested change on top of each 86be4f21 and 1c6aafb5 made
> > no noticeable difference in either of the two behaviors.
> >
> >> If that fails you should compile your kernel with trace events, to get
some debugging info from the fences. I'll post debugging info if this does
not fix it.
> > Happy to gather whatever debug log or tracing data you need :)
> >
>
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