Protecting dser_reset_gens with a lock (Copilot)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: Nikolai-L

kernel/realsense/d4xx.c

@@ -517,20 +517,31 @@ static struct dser_reset_gen dser_reset_gens[MAX_DSER_NUM];
 static atomic_t *ds5_get_reset_gen(struct ds5 *state)
 {
 	int i;
+	int free_idx = -1;
+	atomic_t *gen = &ds5_reset_gen;
 
 	if (state->dser_dev) {
+		mutex_lock(&serdes_lock__);
 		for (i = 0; i < MAX_DSER_NUM; i++) {
-			if (dser_reset_gens[i].dser_dev == state->dser_dev)
-				return &dser_reset_gens[i].gen;
-			if (!dser_reset_gens[i].dser_dev) {
-				dser_reset_gens[i].dser_dev = state->dser_dev;
-				atomic_set(&dser_reset_gens[i].gen, 0);
-				return &dser_reset_gens[i].gen;
+			if (dser_reset_gens[i].dser_dev == state->dser_dev) {
+				gen = &dser_reset_gens[i].gen;
+				goto out_unlock;
 			}
+			if (!dser_reset_gens[i].dser_dev && free_idx < 0)
+				free_idx = i;
+		}
+
+		if (free_idx >= 0) {
+			dser_reset_gens[free_idx].dser_dev = state->dser_dev;
+			atomic_set(&dser_reset_gens[free_idx].gen, 0);
+			gen = &dser_reset_gens[free_idx].gen;
 		}
+out_unlock:
+		mutex_unlock(&serdes_lock__);
 	}
+
 	/* Fallback: table full or no deserializer */
-	return &ds5_reset_gen;
+	return gen;
 }
 #else
 static inline atomic_t *ds5_get_reset_gen(struct ds5 *state)