Claude review: drm/vmwgfx: Don't overwrite KMS surface dirty tracker

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

Patch Review

**Correctness: Good.** The fix is sound. Looking at `vmw_surface_dirty_alloc()` at `vmwgfx_surface.c:2040`:

```c
res->dirty = (struct vmw_resource_dirty *) dirty;
```

This unconditionally overwrites `res->dirty`, so if a dirty tracker was already allocated, the previous allocation is leaked. The guard:

```c
if (surface->res.dirty == NULL)
    ret = surface->res.func->dirty_alloc(&surface->res);
```

correctly prevents the double allocation. This pattern is consistent with the other call site in `vmwgfx_resource.c:402` which also checks `!res->dirty` before calling `dirty_alloc`.

**One minor observation:** The existing code at line 772 already checks `surface->res.func->dirty_alloc` (that the function pointer is non-NULL) before entering the block. It might be slightly cleaner to also set `surface->res.coherent = true` only when the dirty tracker is actually being newly allocated (i.e., move it inside the `if (surface->res.dirty == NULL)` block), since if `dirty` is already allocated, coherent should presumably already be true. However, setting `coherent = true` redundantly is harmless — it's just a boolean assignment — so this is a style nit rather than a bug.

**Commit message and tags: Good.** Has `Reported-by`, `Closes` with lore link, `Fixes` tag referencing the commit that introduced the regression, and proper `Signed-off-by`. All in order.

**Verdict:** The patch is a clean, minimal fix for the reported memory leak. It looks good to merge.

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Generated by Claude Code Patch Reviewer