Claude review: bug/kunit: Reduce runtime impact of warning backtrace suppression

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

Patch Review

**Atomic counter ordering concern (minor)**

```c
+	atomic_inc(&suppressed_warnings_cnt);
 	list_add_rcu(&warning->node, &suppressed_warnings);
```

The counter is incremented before the entry is visible in the list. There's a window where `__kunit_is_suppressed_warning()` sees `counter > 0`, enters the RCU traversal, but doesn't find the entry. This is benign (results in a redundant list walk returning false), but the opposite ordering would be more correct:

```c
	list_add_rcu(&warning->node, &suppressed_warnings);
	atomic_inc(&suppressed_warnings_cnt);
```

Wait - that ordering would also have a problem: the entry could be found before the counter is incremented, but `__kunit_is_suppressed_warning()` checks the counter first, so the entry would never be reached. The current ordering is actually the correct one for this fast-path optimization. The teardown side is fine:

```c
 	list_del_rcu(&warning->node);
 	synchronize_rcu();
+	atomic_dec(&suppressed_warnings_cnt);
```

Decrement after grace period ensures no reader can observe `count == 0` while still seeing the entry. Correct.

**Good separation from patch 1**

Splitting the optimization into its own patch is the right call for reviewability.

---
Generated by Claude Code Patch Reviewer