diff --git a/ipc/sem.c b/ipc/sem.c
index 1ff1032..c14883f5 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -115,7 +115,8 @@ struct sem_queue {
 	struct sembuf		*sops;	 /* array of pending operations */
 	struct sembuf		*blocking; /* the operation that blocked */
 	int			nsops;	 /* number of operations */
-	int			alter;	 /* does *sops alter the array? */
+	bool			alter;	 /* does *sops alter the array? */
+	bool                    dupsop;	 /* sops on more than one sem_num */
 };
 
 /* Each task has a list of undo requests. They are executed automatically
@@ -587,15 +588,23 @@ SYSCALL_DEFINE3(semget, key_t, key, int, nsems, int, semflg)
 }
 
 /**
- * perform_atomic_semop - Perform (if possible) a semaphore operation
+ * perform_atomic_semop[_slow] - Attempt to perform semaphore
+ *                               operations on a given array.
  * @sma: semaphore array
  * @q: struct sem_queue that describes the operation
  *
+ * Caller blocking are as follows, based the value
+ * indicated by the semaphore operation (sem_op):
+ *
+ *  (1) >0 never blocks.
+ *  (2)  0 (wait-for-zero operation): semval is non-zero.
+ *  (3) <0 attempting to decrement semval to a value smaller than zero.
+ *
  * Returns 0 if the operation was possible.
  * Returns 1 if the operation is impossible, the caller must sleep.
- * Negative values are error codes.
+ * Returns <0 for error codes.
  */
-static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
+static int perform_atomic_semop_slow(struct sem_array *sma, struct sem_queue *q)
 {
 	int result, sem_op, nsops, pid;
 	struct sembuf *sop;
@@ -666,6 +675,72 @@ static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
 	return result;
 }
 
+static int perform_atomic_semop(struct sem_array *sma, struct sem_queue *q)
+{
+	int result, sem_op, nsops;
+	struct sembuf *sop;
+	struct sem *curr;
+	struct sembuf *sops;
+	struct sem_undo *un;
+
+	sops = q->sops;
+	nsops = q->nsops;
+	un = q->undo;
+
+	if (unlikely(q->dupsop))
+		return perform_atomic_semop_slow(sma, q);
+
+	/*
+	 * We scan the semaphore set twice, first to ensure that the entire
+	 * operation can succeed, therefore avoiding any pointless writes
+	 * to shared memory and having to undo such changes in order to block
+	 * until the operations can go through.
+	 */
+	for (sop = sops; sop < sops + nsops; sop++) {
+		curr = sma->sem_base + sop->sem_num;
+		sem_op = sop->sem_op;
+		result = curr->semval;
+
+		if (!sem_op && result)
+			goto would_block; /* wait-for-zero */
+
+		result += sem_op;
+		if (result < 0)
+			goto would_block;
+
+		if (result > SEMVMX)
+			return -ERANGE;
+
+		if (sop->sem_flg & SEM_UNDO) {
+			int undo = un->semadj[sop->sem_num] - sem_op;
+
+			/* Exceeding the undo range is an error. */
+			if (undo < (-SEMAEM - 1) || undo > SEMAEM)
+				return -ERANGE;
+		}
+	}
+
+	for (sop = sops; sop < sops + nsops; sop++) {
+		curr = sma->sem_base + sop->sem_num;
+		sem_op = sop->sem_op;
+		result = curr->semval;
+
+		if (sop->sem_flg & SEM_UNDO) {
+			int undo = un->semadj[sop->sem_num] - sem_op;
+
+			un->semadj[sop->sem_num] = undo;
+		}
+		curr->semval += sem_op;
+		curr->sempid = q->pid;
+	}
+
+	return 0;
+
+would_block:
+	q->blocking = sop;
+	return sop->sem_flg & IPC_NOWAIT ? -EAGAIN : 1;
+}
+
 static inline void wake_up_sem_queue_prepare(struct sem_queue *q, int error,
 					     struct wake_q_head *wake_q)
 {
@@ -1720,9 +1795,10 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 	struct sembuf fast_sops[SEMOPM_FAST];
 	struct sembuf *sops = fast_sops, *sop;
 	struct sem_undo *un;
-	int undos = 0, alter = 0, max, locknum;
+	int max, locknum;
+	bool undos = false, alter = false, dupsop = false;
 	struct sem_queue queue;
-	unsigned long jiffies_left = 0;
+	unsigned long dup = 0, jiffies_left = 0;
 	struct ipc_namespace *ns;
 
 	ns = current->nsproxy->ipc_ns;
@@ -1736,10 +1812,12 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 		if (sops == NULL)
 			return -ENOMEM;
 	}
+
 	if (copy_from_user(sops, tsops, nsops * sizeof(*tsops))) {
 		error =  -EFAULT;
 		goto out_free;
 	}
+
 	if (timeout) {
 		struct timespec _timeout;
 		if (copy_from_user(&_timeout, timeout, sizeof(*timeout))) {
@@ -1753,17 +1831,30 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 		}
 		jiffies_left = timespec_to_jiffies(&_timeout);
 	}
+
 	max = 0;
 	for (sop = sops; sop < sops + nsops; sop++) {
+		unsigned long mask = 1ULL << ((sop->sem_num) % BITS_PER_LONG);
+
 		if (sop->sem_num >= max)
 			max = sop->sem_num;
 		if (sop->sem_flg & SEM_UNDO)
-			undos = 1;
-		if (sop->sem_op != 0)
-			alter = 1;
+			undos = true;
+		if (dup & mask) {
+			/*
+			 * There was a previous alter access that appears
+			 * to have accessed the same semaphore, thus use
+			 * the dupsop logic. "appears", because the detection
+			 * can only check % BITS_PER_LONG.
+			 */
+			dupsop = true;
+		}
+		if (sop->sem_op != 0) {
+			alter = true;
+			dup |= mask;
+		}
 	}
 
-
 	if (undos) {
 		/* On success, find_alloc_undo takes the rcu_read_lock */
 		un = find_alloc_undo(ns, semid);
@@ -1828,6 +1919,7 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
 	queue.undo = un;
 	queue.pid = task_tgid_vnr(current);
 	queue.alter = alter;
+	queue.dupsop = dupsop;
 
 	error = perform_atomic_semop(sma, &queue);
 	if (error == 0) { /* non-blocking succesfull path */