ext4: Remove useless spinlock in ext4_getattr()

Linus noted, and complained to me, that doing while lots of "git diff"'s
of kernel sources, these spinlocks were responsible for 27% of the
spinlock cost on his two-processor system as reported by perf.

Git was doing lots of parallel stats, and this was putting a lot of
pressure on ext4_getattr().  A spinlock to protect a single
memory-to-memory copy is pointless, so remove it.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ext4/inode.c

@@ -5410,9 +5410,7 @@ int ext4_getattr(struct vfsmount *mnt, struct dentry *dentry,
 	 * will return the blocks that include the delayed allocation
 	 * blocks for this file.
 	 */
-	spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
 	delalloc_blocks = EXT4_I(inode)->i_reserved_data_blocks;
-	spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
 
 	stat->blocks += (delalloc_blocks << inode->i_sb->s_blocksize_bits)>>9;
 	return 0;