[PATCH] EXT2: Remove superblock lock contention in ext2_statfs

Fix a performance degradation introduced in 2.6.17.  (30% degradation
running dbench with 16 threads)

Commit 21730ee, which claims to make
EXT2_DEBUG work again, moves the taking of the kernel lock out of
debug-only code in ext2_count_free_inodes and ext2_count_free_blocks and
into ext2_statfs.

The same problem was fixed in ext3 by removing the lock completely (commit
5b11687)

Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ext2/balloc.c

@@ -539,7 +539,6 @@ unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
 
 #endif  /*  EXT2FS_DEBUG  */
 
-/* Superblock must be locked */
 unsigned long ext2_count_free_blocks (struct super_block * sb)
 {
 	struct ext2_group_desc * desc;

fs/ext2/ialloc.c

@@ -637,7 +637,6 @@ struct inode *ext2_new_inode(struct inode *dir, int mode)
 	return ERR_PTR(err);
 }
 
-/* Superblock must be locked */
 unsigned long ext2_count_free_inodes (struct super_block * sb)
 {
 	struct ext2_group_desc *desc;

fs/ext2/super.c

@@ -1083,7 +1083,6 @@ static int ext2_statfs (struct dentry * dentry, struct kstatfs * buf)
 	unsigned long overhead;
 	int i;
 
-	lock_super(sb);
 	if (test_opt (sb, MINIX_DF))
 		overhead = 0;
 	else {
@@ -1124,7 +1123,6 @@ static int ext2_statfs (struct dentry * dentry, struct kstatfs * buf)
 	buf->f_files = le32_to_cpu(sbi->s_es->s_inodes_count);
 	buf->f_ffree = ext2_count_free_inodes (sb);
 	buf->f_namelen = EXT2_NAME_LEN;
-	unlock_super(sb);
 	return 0;
 }