srcu: Fix error handling in init_srcu_struct_fields()

The current error handling in init_srcu_struct_fields() is a bit
inconsistent.  If init_srcu_struct_nodes() fails, the function either
returns -ENOMEM or 0 depending on whether ssp->sda_is_static is true or
false. This can make init_srcu_struct_fields() return 0 even if memory
allocation failed!

Simplify the error handling by always returning -ENOMEM if either
init_srcu_struct_nodes() or the per-CPU allocation fails. This makes the
control flow easier to follow and avoids the inconsistent return values.

Add goto labels to avoid duplicating the error cleanup code.

Link: https://lore.kernel.org/r/20230404003508.GA254019@google.com
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

Author: joelagnel

kernel/rcu/srcutree.c

@@ -255,29 +255,31 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
 	ssp->srcu_sup->sda_is_static = is_static;
 	if (!is_static)
 		ssp->sda = alloc_percpu(struct srcu_data);
-	if (!ssp->sda) {
-		if (!is_static)
-			kfree(ssp->srcu_sup);
-		return -ENOMEM;
-	}
+	if (!ssp->sda)
+		goto err_free_sup;
 	init_srcu_struct_data(ssp);
 	ssp->srcu_sup->srcu_gp_seq_needed_exp = 0;
 	ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
 	if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
-		if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) {
-			if (!ssp->srcu_sup->sda_is_static) {
-				free_percpu(ssp->sda);
-				ssp->sda = NULL;
-				kfree(ssp->srcu_sup);
-				return -ENOMEM;
-			}
-		} else {
-			WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
-		}
+		if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
+			goto err_free_sda;
+		WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
 	}
 	ssp->srcu_sup->srcu_ssp = ssp;
 	smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */
 	return 0;
+
+err_free_sda:
+	if (!is_static) {
+		free_percpu(ssp->sda);
+		ssp->sda = NULL;
+	}
+err_free_sup:
+	if (!is_static) {
+		kfree(ssp->srcu_sup);
+		ssp->srcu_sup = NULL;
+	}
+	return -ENOMEM;
 }
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC