ext2/3: use prandom_u32() instead of get_random_bytes()

Many of the uses of get_random_bytes() do not actually need
cryptographically secure random numbers.  Replace those uses with a
call to prandom_u32(), which is faster and which doesn't consume
entropy from the /dev/random driver.

The commit dd1f723bf56bd96efc9d90e9e60dc511c79de48f has made that for
ext4, and i did the same for ext2/3.

Signed-off-by: Zhang Zhen <zhenzhang.zhang@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext2/ialloc.c

@@ -284,7 +284,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent)
 		int best_ndir = inodes_per_group;
 		int best_group = -1;
 
-		get_random_bytes(&group, sizeof(group));
+		group = prandom_u32();
 		parent_group = (unsigned)group % ngroups;
 		for (i = 0; i < ngroups; i++) {
 			group = (parent_group + i) % ngroups;

fs/ext3/ialloc.c

@@ -215,7 +215,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent)
 		int best_ndir = inodes_per_group;
 		int best_group = -1;
 
-		get_random_bytes(&group, sizeof(group));
+		group = prandom_u32();
 		parent_group = (unsigned)group % ngroups;
 		for (i = 0; i < ngroups; i++) {
 			group = (parent_group + i) % ngroups;