Claude review: drm/modeset_lock: add NULL check for ctx before WARN_ON

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

Patch Review

**NAK.**

The change:
```c
-	if (WARN_ON(ctx->contended))
+	if (ctx && WARN_ON(ctx->contended))
```

**Problem 1: The guard is unnecessary.** As discussed above, `modeset_lock()` is a static helper only called from `drm_modeset_lock()` (which already NULL-checks `ctx` before calling it) and `drm_modeset_backoff()` (which dereferences `ctx` before calling it). There is no path where `ctx` is NULL here.

**Problem 2: The patch is incomplete even on its own terms.** It guards the `ctx->contended` dereference on line 298, but the very next line that uses `ctx` is:
```c
	if (ctx->trylock_only) {
```
This dereference at line 301 is left completely unguarded. If `ctx` truly could be NULL, this patch would still crash two lines later. Patch 1 in isolation does not produce a correct result.

**Problem 3: Inaccurate commit message.** The commit message says "modeset_lock() and drm_modeset_drop_locks() do not validate the ctx pointer" but neither this patch nor patch 2 modifies `drm_modeset_drop_locks()`.

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Generated by Claude Code Patch Reviewer