Btrfs: Fix an off by one in the extent_map prepare write code

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/extent_map.c

@@ -2279,7 +2279,7 @@ int extent_prepare_write(struct extent_map_tree *tree,
 			u64 extent_offset = block_start - em->start;
 			size_t iosize;
 			sector = (em->block_start + extent_offset) >> 9;
-			iosize = (cur_end - block_start + blocksize - 1) &
+			iosize = (cur_end - block_start + blocksize) &
 				~((u64)blocksize - 1);
 			/*
 			 * we've already got the extent locked, but we

fs/btrfs/inode.c

@@ -1956,7 +1956,7 @@ static int btrfs_prepare_write(struct file *file, struct page *page,
 
 	mutex_lock(&root->fs_info->fs_mutex);
 	err = btrfs_check_free_space(root, PAGE_CACHE_SIZE, 0);
-	mutex_lock(&root->fs_info->fs_mutex);
+	mutex_unlock(&root->fs_info->fs_mutex);
 	if (err)
 		return -ENOSPC;