ext4: 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.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

3 files changed, 4 insertions, 7 deletions

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index 137193ff389b..0ee59a6644e2 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -432,7 +432,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent,
                         ext4fs_dirhash(qstr->name, qstr->len, &hinfo);
                         grp = hinfo.hash;
                 } else
-                        get_random_bytes(&grp, sizeof(grp));
+                        grp = prandom_u32();
                 parent_group = (unsigned)grp % ngroups;
                 for (i = 0; i < ngroups; i++) {
                         g = (parent_group + i) % ngroups;
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 214461e42a05..04434ad3e8e0 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -259,7 +259,7 @@ static unsigned int mmp_new_seq(void)
         u32 new_seq;
 
         do {
-                get_random_bytes(&new_seq, sizeof(u32));
+                new_seq = prandom_u32();
         } while (new_seq > EXT4_MMP_SEQ_MAX);
 
         return new_seq;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d3a857bfae47..c977f4e4e63b 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3068,7 +3068,6 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
 {
         struct ext4_sb_info *sbi = EXT4_SB(sb);
         struct ext4_li_request *elr;
-        unsigned long rnd;
 
         elr = kzalloc(sizeof(*elr), GFP_KERNEL);
         if (!elr)
@@ -3083,10 +3082,8 @@ static struct ext4_li_request *ext4_li_request_new(struct super_block *sb,
          * spread the inode table initialization requests
          * better.
          */
-        get_random_bytes(&rnd, sizeof(rnd));
-        elr->lr_next_sched = jiffies + (unsigned long)rnd %
-                             (EXT4_DEF_LI_MAX_START_DELAY * HZ);
-
+        elr->lr_next_sched = jiffies + (prandom_u32() %
+                                (EXT4_DEF_LI_MAX_START_DELAY * HZ));
         return elr;
 }