LoadPin: Move pin reporting cleanly out of locking

Refactor the pin reporting to be more cleanly outside the locking. It
was already, but moving it around helps clear the path for the root to
switch when not enforcing.

Cc: Paul Moore <paul@paul-moore.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20221209195746.1366607-3-keescook@chromium.org

security/loadpin/loadpin.c

@@ -131,6 +131,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 {
 	struct super_block *load_root;
 	const char *origin = kernel_read_file_id_str(id);
+	bool first_root_pin = false;
 	bool load_root_writable;
 
 	/* If the file id is excluded, ignore the pinning. */
@@ -162,18 +163,14 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 	 */
 	if (!pinned_root) {
 		pinned_root = load_root;
-		/*
-		 * Unlock now since it's only pinned_root we care about.
-		 * In the worst case, we will (correctly) report pinning
-		 * failures before we have announced that pinning is
-		 * enforcing. This would be purely cosmetic.
-		 */
+		first_root_pin = true;
+	}
 	spin_unlock(&pinned_root_spinlock);
+
+	if (first_root_pin) {
 		report_writable(pinned_root, load_root_writable);
 		set_sysctl(load_root_writable);
 		report_load(origin, file, "pinned");
-	} else {
-		spin_unlock(&pinned_root_spinlock);
 	}
 
 	if (IS_ERR_OR_NULL(pinned_root) ||