Claude review: dma-fence: Clarify external lock use case in dma_fence_init() docs

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

Patch Review

**Assessment: Good patch, minor nit.**

The commit message explains the rationale well:

> a shared spinlock does not (and cannot) prevent the signaler from signaling out of order. Signaling order is the driver's responsibility regardless of whether the lock is shared or per-fence.
>
> What a shared lock actually provides is serialization of signaling and observation across fences in a given context, so that observers never see a later fence signaled while an earlier one is not.

This is correct. Looking at `dma_fence_signal()` (line 487), it acquires the fence lock, then calls `dma_fence_signal_timestamp_locked()`. If two fences share a lock, signaling one will block until the other's signal+callback processing completes, ensuring observers under the same lock see a consistent ordering.

The code change itself:

```c
- * lock and fence life time. This is only allowed for legacy use cases when
- * multiple fences need to be prevented from signaling out of order.
+ * lock and fence lifetime. This is only allowed for legacy use cases that need
+ * a shared lock to serialize signaling and observation of fences within a
+ * context, so that observers never see a later fence signaled while an earlier
+ * one isn't.
```

This is applied identically to both `dma_fence_init()` and `dma_fence_init64()`, which is correct since they share the same doc structure.

**Minor nit:** The fix of "life time" → "lifetime" is a nice bonus typo fix. It might be worth calling that out in the commit message so reviewers know it's intentional, though it's trivially obvious.

**One small wording suggestion:** The phrase "one isn't" at the end is slightly informal for kernel documentation. Consider "one is not" for consistency with the formal tone of the rest of the doc comment. This is purely stylistic and not a blocking concern.

**Reviewed-by worthy: Yes.** The patch is correct, well-explained, and improves clarity. The cover letter also shows good engagement with the community by inviting feedback on the interpretation.

---
Generated by Claude Code Patch Reviewer