[PATCH 2/3] Revert "drm/i915: Propagate errors on awaiting already signaled fences" - Linux-stable-mirror

5 May 2022

From: Jason Ekstrand jason@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.
For backporters: Please note that you _must_ have a backport of
https://lore.kernel.org/dri-devel/20210602164149.391653-2-jason@jlekstrand.n...
for otherwise backporting just this patch opens up a security bug.
v2: Augment commit message. Also restore Jason's sob that I
accidentally lost.
v3: Add a note for backporters
Signed-off-by: Jason Ekstrand jason@jlekstrand.net
Reported-by: Marcin Slusarz marcin.slusarz@intel.com
Cc: stable@vger.kernel.org # v5.6+
Cc: Jason Ekstrand jason.ekstrand@intel.com
Cc: Marcin Slusarz marcin.slusarz@intel.com
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3080
Fixes: 9e31c1fe45d5 ("drm/i915: Propagate errors on awaiting already signaled fences")
Acked-by: Daniel Vetter daniel.vetter@ffwll.ch
Reviewed-by: Jon Bloomfield jon.bloomfield@intel.com
Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch
Link: https://patchwork.freedesktop.org/patch/msgid/20210714193419.1459723-3-jason...
(cherry picked from commit 93a2711cddd5760e2f0f901817d71c93183c3b87)
---
 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 8bd484e2a0ec..08484c14d11e 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

    