Claude review: drm/imagination: acquire vm_ctx->lock before mapping memory to GPU VM

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

Patch Review

**Bug: Double `mutex_unlock` on the success path**

After applying the patch, the success path through `pvr_vm_map()` executes:

```c
	mutex_lock(&vm_ctx->lock);          // line 750: acquire
	err = drm_gpuvm_exec_lock(&vm_exec);
	// ... succeeds, no goto ...

	err = pvr_vm_bind_op_exec(&bind_op);

	drm_gpuvm_exec_unlock(&vm_exec);
	mutex_unlock(&vm_ctx->lock);        // line 758: first unlock

err_cleanup:
	pvr_vm_bind_op_fini(&bind_op);
	mutex_unlock(&vm_ctx->lock);        // line 762: SECOND unlock — BUG
```

On success, execution falls through past the first `mutex_unlock` at line 758 into `err_cleanup:`, where the mutex is unlocked a **second time**. This is undefined behavior for a non-recursive mutex — it corrupts the mutex state, can cause subsequent lock attempts to succeed without mutual exclusion, or trigger a `DEBUG_LOCKS_WARN_ON` splat. This effectively trades a NULL dereference race for a lock corruption bug.

The error path (where `drm_gpuvm_exec_lock` fails and jumps to `err_cleanup`) is correct — the mutex is only unlocked once.

**Fix:** Remove the `mutex_unlock` after `drm_gpuvm_exec_unlock()` and keep only the single unlock at `err_cleanup`. This mirrors the structure used in `pvr_vm_unmap_obj_locked()` (lines 800–819) where the cleanup path is the only exit:

```c
	mutex_lock(&vm_ctx->lock);
	err = drm_gpuvm_exec_lock(&vm_exec);
	if (err)
		goto err_cleanup;

	err = pvr_vm_bind_op_exec(&bind_op);

	drm_gpuvm_exec_unlock(&vm_exec);

err_cleanup:
	pvr_vm_bind_op_fini(&bind_op);
	mutex_unlock(&vm_ctx->lock);

	return err;
```

**Minor nit:** The commit message says "all occurences" (should be "occurrences") and "NULL deference" (should be "dereference").

**Verdict:** The intent is correct and the fix is needed, but the implementation has a critical double-unlock bug. NAK in current form; a v3 with the single-unlock-point fix described above should be straightforward.

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Generated by Claude Code Patch Reviewer