mac80211: fix deadlocks in debugfs_netdev.c

The bug shows up with CONFIG_PREEMPT enabled. Pointed out by Andrew Morton.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Luis Carlos Cobo <luisca@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/mac80211/debugfs_netdev.c

@@ -31,11 +31,13 @@ static ssize_t ieee80211_if_read(
 	ssize_t ret = -EINVAL;
 
 	read_lock(&dev_base_lock);
-	if (sdata->dev->reg_state == NETREG_REGISTERED) {
+	if (sdata->dev->reg_state == NETREG_REGISTERED)
 		ret = (*format)(sdata, buf, sizeof(buf));
-		ret = simple_read_from_buffer(userbuf, count, ppos, buf, ret);
-	}
 	read_unlock(&dev_base_lock);
+
+	if (ret != -EINVAL)
+		ret = simple_read_from_buffer(userbuf, count, ppos, buf, ret);
+
 	return ret;
 }
 
@@ -51,13 +53,13 @@ static ssize_t ieee80211_if_write(
 
 	memset(buf, 0x00, sizeof(buf));
 	buf_size = min(count, (sizeof(buf)-1));
-	read_lock(&dev_base_lock);
 	if (copy_from_user(buf, userbuf, buf_size))
-		goto endwrite;
+		return count;
+	read_lock(&dev_base_lock);
 	if (sdata->dev->reg_state == NETREG_REGISTERED)
 		(*format)(sdata, buf);
-endwrite:
 	read_unlock(&dev_base_lock);
+
 	return count;
 }
 #endif