cxl: Fix afu_read() not doing finish_wait() on signal or non-blocking

If afu_read() returned due to a signal or the AFU file descriptor being
opened non-blocking it would not call finish_wait() before returning,
which could lead to a crash later when something else wakes up the wait
queue.

This patch restructures the wait logic to ensure that the cleanup is
done correctly.

Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/file.c

@@ -273,6 +273,7 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 	struct cxl_context *ctx = file->private_data;
 	struct cxl_event event;
 	unsigned long flags;
+	int rc;
 	DEFINE_WAIT(wait);
 
 	if (count < CXL_READ_MIN_SIZE)
@@ -285,13 +286,17 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 		if (ctx_event_pending(ctx))
 			break;
 
-		spin_unlock_irqrestore(&ctx->lock, flags);
-		if (file->f_flags & O_NONBLOCK)
-			return -EAGAIN;
+		if (file->f_flags & O_NONBLOCK) {
+			rc = -EAGAIN;
+			goto out;
+		}
 
-		if (signal_pending(current))
-			return -ERESTARTSYS;
+		if (signal_pending(current)) {
+			rc = -ERESTARTSYS;
+			goto out;
+		}
 
+		spin_unlock_irqrestore(&ctx->lock, flags);
 		pr_devel("afu_read going to sleep...\n");
 		schedule();
 		pr_devel("afu_read woken up\n");
@@ -336,6 +341,11 @@ static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
 	if (copy_to_user(buf, &event, event.header.size))
 		return -EFAULT;
 	return event.header.size;
+
+out:
+	finish_wait(&ctx->wq, &wait);
+	spin_unlock_irqrestore(&ctx->lock, flags);
+	return rc;
 }
 
 static const struct file_operations afu_fops = {