Claude review: drm/i915/gt: Use IS_ERR() check for kernel_context() in selftests

[Claude Code Review Bot <claude-review@example.com>]

Overall Series Review

Subject: drm/i915/gt: Use IS_ERR() check for kernel_context() in selftests
Author: Ingyu Jang <ingyujang25@korea.ac.kr>
Patches: 1
Reviewed: 2026-05-16T10:29:02.406576

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**Verdict: Correct fix, but incomplete — misses one call site in the same file.**

The patch correctly identifies a real bug: `kernel_context()` (defined in `gem/selftests/mock_context.c`) returns `ERR_PTR` on failure (via `ERR_CAST` from `proto_context_create()` or directly from `i915_gem_create_context()`), never `NULL`. The existing `!ctx` checks would silently pass an `ERR_PTR` through, leading to a kernel oops on the very next dereference (e.g., `ctx_hi->sched.priority = ...`).

The transformation is mechanically correct in all four locations touched. However, the patch misses one more instance of the same bug in the same file at line 3685-3687 in `live_preempt_smoke()`:

```c
smoke.contexts[n] = kernel_context(smoke.gt->i915, NULL);
if (!smoke.contexts[n])
    goto err_ctx;
```

This should also be converted to `IS_ERR()` / `PTR_ERR()` for completeness, and `err_ctx` cleanup would need to handle passing an `ERR_PTR` in the `smoke.contexts[]` array (the cleanup loop calls `kernel_context_close()` on each non-NULL entry, so an `ERR_PTR` value would also be dereferenced there).

There may also be similar incorrect NULL checks in other selftest files (e.g., `selftest_hangcheck.c`, `selftest_workarounds.c`, `selftest_lrc.c`, etc.) that call `kernel_context()`. A v2 with broader scope would be more useful.

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