diff --git a/crypto/drbg.c b/crypto/drbg.c
index 2a7860f..a76b3cb 100644
--- a/crypto/drbg.c
+++ b/crypto/drbg.c
@@ -646,7 +646,7 @@
 /* Generate function of CTR DRBG as defined in 10.2.1.5.2 */
 static int drbg_ctr_generate(struct drbg_state *drbg,
 			     unsigned char *buf, unsigned int buflen,
-			     struct drbg_string *addtl)
+			     struct list_head *addtl)
 {
 	int len = 0;
 	int ret = 0;
@@ -656,11 +656,8 @@
 	memset(drbg->scratchpad, 0, drbg_blocklen(drbg));
 
 	/* 10.2.1.5.2 step 2 */
-	if (addtl && 0 < addtl->len) {
-		LIST_HEAD(addtllist);
-
-		list_add_tail(&addtl->list, &addtllist);
-		ret = drbg_ctr_update(drbg, &addtllist, 2);
+	if (addtl && !list_empty(addtl)) {
+		ret = drbg_ctr_update(drbg, addtl, 2);
 		if (ret)
 			return 0;
 	}
@@ -777,7 +774,7 @@
 static int drbg_hmac_generate(struct drbg_state *drbg,
 			      unsigned char *buf,
 			      unsigned int buflen,
-			      struct drbg_string *addtl)
+			      struct list_head *addtl)
 {
 	int len = 0;
 	int ret = 0;
@@ -785,11 +782,8 @@
 	LIST_HEAD(datalist);
 
 	/* 10.1.2.5 step 2 */
-	if (addtl && 0 < addtl->len) {
-		LIST_HEAD(addtllist);
-
-		list_add_tail(&addtl->list, &addtllist);
-		ret = drbg_hmac_update(drbg, &addtllist, 1);
+	if (addtl && !list_empty(addtl)) {
+		ret = drbg_hmac_update(drbg, addtl, 1);
 		if (ret)
 			return ret;
 	}
@@ -813,14 +807,10 @@
 	}
 
 	/* 10.1.2.5 step 6 */
-	if (addtl && 0 < addtl->len) {
-		LIST_HEAD(addtllist);
-
-		list_add_tail(&addtl->list, &addtllist);
-		ret = drbg_hmac_update(drbg, &addtllist, 1);
-	} else {
+	if (addtl && !list_empty(addtl))
+		ret = drbg_hmac_update(drbg, addtl, 1);
+	else
 		ret = drbg_hmac_update(drbg, NULL, 1);
-	}
 	if (ret)
 		return ret;
 
@@ -944,7 +934,7 @@
 
 /* processing of additional information string for Hash DRBG */
 static int drbg_hash_process_addtl(struct drbg_state *drbg,
-				   struct drbg_string *addtl)
+				   struct list_head *addtl)
 {
 	int ret = 0;
 	struct drbg_string data1, data2;
@@ -955,7 +945,7 @@
 	memset(drbg->scratchpad, 0, drbg_blocklen(drbg));
 
 	/* 10.1.1.4 step 2 */
-	if (!addtl || 0 == addtl->len)
+	if (!addtl || list_empty(addtl))
 		return 0;
 
 	/* 10.1.1.4 step 2a */
@@ -963,7 +953,7 @@
 	drbg_string_fill(&data2, drbg->V, drbg_statelen(drbg));
 	list_add_tail(&data1.list, &datalist);
 	list_add_tail(&data2.list, &datalist);
-	list_add_tail(&addtl->list, &datalist);
+	list_splice_tail(addtl, &datalist);
 	ret = drbg_kcapi_hash(drbg, NULL, drbg->scratchpad, &datalist);
 	if (ret)
 		goto out;
@@ -1029,7 +1019,7 @@
 /* generate function for Hash DRBG as defined in  10.1.1.4 */
 static int drbg_hash_generate(struct drbg_state *drbg,
 			      unsigned char *buf, unsigned int buflen,
-			      struct drbg_string *addtl)
+			      struct list_head *addtl)
 {
 	int len = 0;
 	int ret = 0;
@@ -1347,6 +1337,12 @@
 {
 	int len = 0;
 	struct drbg_state *shadow = NULL;
+	LIST_HEAD(addtllist);
+	struct drbg_string timestamp;
+	union {
+		cycles_t cycles;
+		unsigned char char_cycles[sizeof(cycles_t)];
+	} now;
 
 	if (0 == buflen || !buf) {
 		pr_devel("DRBG: no output buffer provided\n");
@@ -1407,8 +1403,23 @@
 		/* 9.3.1 step 7.4 */
 		addtl = NULL;
 	}
+
+	/*
+	 * Mix the time stamp into the DRBG state if the DRBG is not in
+	 * test mode. If there are two callers invoking the DRBG at the same
+	 * time, i.e. before the first caller merges its shadow state back,
+	 * both callers would obtain the same random number stream without
+	 * changing the state here.
+	 */
+	if (!drbg->test_data) {
+		now.cycles = random_get_entropy();
+		drbg_string_fill(&timestamp, now.char_cycles, sizeof(cycles_t));
+		list_add_tail(&timestamp.list, &addtllist);
+	}
+	if (addtl && 0 < addtl->len)
+		list_add_tail(&addtl->list, &addtllist);
 	/* 9.3.1 step 8 and 10 */
-	len = shadow->d_ops->generate(shadow, buf, buflen, addtl);
+	len = shadow->d_ops->generate(shadow, buf, buflen, &addtllist);
 
 	/* 10.1.1.4 step 6, 10.1.2.5 step 7, 10.2.1.5.2 step 7 */
 	shadow->reseed_ctr++;
diff --git a/include/crypto/drbg.h b/include/crypto/drbg.h
index 4065dfc..831d786 100644
--- a/include/crypto/drbg.h
+++ b/include/crypto/drbg.h
@@ -102,7 +102,7 @@
 		      int reseed);
 	int (*generate)(struct drbg_state *drbg,
 			unsigned char *buf, unsigned int buflen,
-			struct drbg_string *addtl);
+			struct list_head *addtl);
 	int (*crypto_init)(struct drbg_state *drbg);
 	int (*crypto_fini)(struct drbg_state *drbg);