[PATCH] Revert "drm/i915: Propagate errors on awaiting already signaled fences"

[Daniel Vetter]

On Wed, May 19, 2021 at 5:06 PM Jason Ekstrand <jason at jlekstrand.net> wrote:
>
> Once we no longer rely on error propagation, I think there's a lot we
> can rip out.

I honestly did not find that much ... what did you uncover?
-Daniel

>
> --Jason
>
> On Wed, May 19, 2021 at 5:15 AM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> >
> > From: Jason Ekstrand <jason at jlekstrand.net>
> >
> > This reverts commit 9e31c1fe45d555a948ff66f1f0e3fe1f83ca63f7.  Ever
> > since that commit, we've been having issues where a hang in one client
> > can propagate to another.  In particular, a hang in an app can propagate
> > to the X server which causes the whole desktop to lock up.
> >
> > Error propagation along fences sound like a good idea, but as your bug
> > shows, surprising consequences, since propagating errors across security
> > boundaries is not a good thing.
> >
> > What we do have is track the hangs on the ctx, and report information to
> > userspace using RESET_STATS. That's how arb_robustness works. Also, if my
> > understanding is still correct, the EIO from execbuf is when your context
> > is banned (because not recoverable or too many hangs). And in all these
> > cases it's up to userspace to figure out what is all impacted and should
> > be reported to the application, that's not on the kernel to guess and
> > automatically propagate.
> >
> > What's more, we're also building more features on top of ctx error
> > reporting with RESET_STATS ioctl: Encrypted buffers use the same, and the
> > userspace fence wait also relies on that mechanism. So it is the path
> > going forward for reporting gpu hangs and resets to userspace.
> >
> > So all together that's why I think we should just bury this idea again as
> > not quite the direction we want to go to, hence why I think the revert is
> > the right option here.Signed-off-by: Jason Ekstrand <jason.ekstrand at intel.com>
> >
> > v2: Augment commit message. Also restore Jason's sob that I
> > accidentally lost.
> >
> > Signed-off-by: Jason Ekstrand <jason.ekstrand at intel.com> (v1)
> > Reported-by: Marcin Slusarz <marcin.slusarz at intel.com>
> > Cc: <stable at vger.kernel.org> # v5.6+
> > Cc: Jason Ekstrand <jason.ekstrand at intel.com>
> > Cc: Marcin Slusarz <marcin.slusarz at intel.com>
> > Cc: Jon Bloomfield <jon.bloomfield at intel.com>
> > Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3080
> > Fixes: 9e31c1fe45d5 ("drm/i915: Propagate errors on awaiting already signaled fences")
> > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> > ---
> >  drivers/gpu/drm/i915/i915_request.c | 8 ++------
> >  1 file changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> > index 970d8f4986bb..b796197c0772 100644
> > --- a/drivers/gpu/drm/i915/i915_request.c
> > +++ b/drivers/gpu/drm/i915/i915_request.c
> > @@ -1426,10 +1426,8 @@ i915_request_await_execution(struct i915_request *rq,
> >
> >         do {
> >                 fence = *child++;
> > -               if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> > -                       i915_sw_fence_set_error_once(&rq->submit, fence->error);
> > +               if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> >                         continue;
> > -               }
> >
> >                 if (fence->context == rq->fence.context)
> >                         continue;
> > @@ -1527,10 +1525,8 @@ i915_request_await_dma_fence(struct i915_request *rq, struct dma_fence *fence)
> >
> >         do {
> >                 fence = *child++;
> > -               if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)) {
> > -                       i915_sw_fence_set_error_once(&rq->submit, fence->error);
> > +               if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags))
> >                         continue;
> > -               }
> >
> >                 /*
> >                  * Requests on the same timeline are explicitly ordered, along
> > --
> > 2.31.0
> >



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch