ext4: Remove i_mutex use from ext4_quota_write()

We don't need i_mutex in ext4_quota_write() because writes to quota file
are serialized by dqio_mutex anyway. Changes to quota files outside of quota
code are forbidded and enforced by NOATIME and IMMUTABLE bits.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext4/super.c

@@ -4760,7 +4760,6 @@ static ssize_t ext4_quota_write(struct super_block *sb, int type,
 		return -EIO;
 	}
 
-	mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
 	bh = ext4_bread(handle, inode, blk, 1, &err);
 	if (!bh)
 		goto out;
@@ -4776,16 +4775,13 @@ static ssize_t ext4_quota_write(struct super_block *sb, int type,
 	err = ext4_handle_dirty_metadata(handle, NULL, bh);
 	brelse(bh);
 out:
-	if (err) {
-		mutex_unlock(&inode->i_mutex);
+	if (err)
 		return err;
-	}
 	if (inode->i_size < off + len) {
 		i_size_write(inode, off + len);
 		EXT4_I(inode)->i_disksize = inode->i_size;
 		ext4_mark_inode_dirty(handle, inode);
 	}
-	mutex_unlock(&inode->i_mutex);
 	return len;
 }