drm/nouveau: Fix WARN_ON in nouveau_fence_context_kill()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/nouveau: Fix WARN_ON in nouveau_fence_context_kill() Nouveau is mostly designed in a way that it's expected that fences only ever get signaled through nouveau_fence_signal(). However, in at least one other place, nouveau_fence_done(), can signal fences, too. If that happens (race) a signaled fence remains in the pending list for a while, until it gets removed by nouveau_fence_update(). Should nouveau_fence_context_kill() run in the meantime, this would be a bug because the function would attempt to set an error code on an already signaled fence. Have nouveau_fence_context_kill() check for a fence being signaled.

References

• https://git.kernel.org/stable/c/39d6e889c0b19a2c79e1c74c843ea7c2d0f99c28
• https://git.kernel.org/stable/c/2ec0f5f6d4768f292c8406ed92fa699f184577e5
• https://git.kernel.org/stable/c/47ca11836c35c5698088fd87f7fb4b0ffa217e17
• https://git.kernel.org/stable/c/126f5c6e0cb84e5c6f7a3a856d799d85668fb38e
• https://git.kernel.org/stable/c/b771b2017260ffc3a8d4e81266619649bffcb242
• https://git.kernel.org/stable/c/0453825167ecc816ec15c736e52316f69db0deb9
• https://git.kernel.org/stable/c/bbe5679f30d7690a9b6838a583b9690ea73fe0e9