diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 6cdef9d5f8d0..f4a197b2d1fd 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -1413,22 +1413,19 @@ static int do_cmd_ioctl(struct comedi_device *dev,
 		DPRINTK("subdevice busy\n");
 		return -EBUSY;
 	}
-	s->busy = file;
 
 	/* make sure channel/gain list isn't too long */
 	if (cmd.chanlist_len > s->len_chanlist) {
 		DPRINTK("channel/gain list too long %u > %d\n",
 			cmd.chanlist_len, s->len_chanlist);
-		ret = -EINVAL;
-		goto cleanup;
+		return -EINVAL;
 	}
 
 	/* make sure channel/gain list isn't too short */
 	if (cmd.chanlist_len < 1) {
 		DPRINTK("channel/gain list too short %u < 1\n",
 			cmd.chanlist_len);
-		ret = -EINVAL;
-		goto cleanup;
+		return -EINVAL;
 	}
 
 	async->cmd = cmd;
@@ -1438,8 +1435,7 @@ static int do_cmd_ioctl(struct comedi_device *dev,
 	    kmalloc(async->cmd.chanlist_len * sizeof(int), GFP_KERNEL);
 	if (!async->cmd.chanlist) {
 		DPRINTK("allocation failed\n");
-		ret = -ENOMEM;
-		goto cleanup;
+		return -ENOMEM;
 	}
 
 	if (copy_from_user(async->cmd.chanlist, user_chanlist,
@@ -1491,6 +1487,9 @@ static int do_cmd_ioctl(struct comedi_device *dev,
 
 	comedi_set_subdevice_runflags(s, ~0, SRF_USER | SRF_RUNNING);
 
+	/* set s->busy _after_ setting SRF_RUNNING flag to avoid race with
+	 * comedi_read() or comedi_write() */
+	s->busy = file;
 	ret = s->do_cmd(dev, s);
 	if (ret == 0)
 		return 0;
@@ -2058,11 +2057,13 @@ static ssize_t comedi_write(struct file *file, const char __user *buf,
 
 		if (!comedi_is_subdevice_running(s)) {
 			if (count == 0) {
+				mutex_lock(&dev->mutex);
 				if (comedi_is_subdevice_in_error(s))
 					retval = -EPIPE;
 				else
 					retval = 0;
 				do_become_nonbusy(dev, s);
+				mutex_unlock(&dev->mutex);
 			}
 			break;
 		}
@@ -2161,11 +2162,13 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 
 		if (n == 0) {
 			if (!comedi_is_subdevice_running(s)) {
+				mutex_lock(&dev->mutex);
 				do_become_nonbusy(dev, s);
 				if (comedi_is_subdevice_in_error(s))
 					retval = -EPIPE;
 				else
 					retval = 0;
+				mutex_unlock(&dev->mutex);
 				break;
 			}
 			if (file->f_flags & O_NONBLOCK) {
@@ -2203,9 +2206,11 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 		buf += n;
 		break;		/* makes device work like a pipe */
 	}
-	if (comedi_is_subdevice_idle(s) &&
-	    async->buf_read_count - async->buf_write_count == 0) {
-		do_become_nonbusy(dev, s);
+	if (comedi_is_subdevice_idle(s)) {
+		mutex_lock(&dev->mutex);
+		if (async->buf_read_count - async->buf_write_count == 0)
+			do_become_nonbusy(dev, s);
+		mutex_unlock(&dev->mutex);
 	}
 	set_current_state(TASK_RUNNING);
 	remove_wait_queue(&async->wait_head, &wait);