drm/i915: skip __i915_request_skip() for already signaled requests

After a GPU reset the HWSP is zeroed, so previously completed
requests appear incomplete. If such a request is picked up during
reset_rewind() and marked guilty, i915_request_set_error_once()
returns early (fence already signaled), leaving fence.error without
a fatal error code. The subsequent __i915_request_skip() then hits:
```
GEM_BUG_ON(!fatal_error(rq->fence.error))
```

Fixes a kernel BUG observed on Sandy Bridge (Gen6) during
heartbeat-triggered engine resets.
```
kernel BUG at drivers/gpu/drm/i915/i915_request.c:556!
RIP: __i915_request_skip+0x15e/0x1d0 [i915]
...
__i915_request_reset+0x212/0xa70 [i915]
reset_rewind+0xe4/0x280 [i915]
intel_gt_reset+0x30d/0x5b0 [i915]
heartbeat+0x516/0x530 [i915]
```

Guard __i915_request_skip() with i915_request_signaled(), if the
fence is already signaled, the ring content is committed and there
is nothing left to skip.

Fixes: 36e191f0644b ("drm/i915: Apply i915_request_skip() on submission")
Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/13729
Signed-off-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
Cc: stable@vger.kernel.org # v5.7+
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/fe76921d35b6ae85aa651822726d0d9815aa5362.1776339012.git.sebastian.brzezinka@intel.com
(cherry picked from commit 5ba54393dcd7adf75a9f39f5a933b1538349cad5)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>

0 files changed, 0 insertions, 0 deletions