xfs: reduce ilock hold times in xfs_setattr_size

We do not need the ilock for most checks done in the beginning of
xfs_setattr_size.  Replace the long critical section before starting the
transaction with a smaller one around xfs_zero_eof and an optional one
inside xfs_qm_dqattach that isn't entered unless using quotas.  While
this isn't a big optimization for xfs_setattr_size itself it will allow
pushing the ilock into xfs_zero_eof itself later.
Signed-off-by: NChristoph Hellwig <hch@lst.de>

fs/xfs/xfs_iops.c

@@ -700,7 +700,7 @@ xfs_setattr_size(
 	xfs_off_t		oldsize, newsize;
 	struct xfs_trans	*tp;
 	int			error;
-	uint			lock_flags;
+	uint			lock_flags = 0;
 	uint			commit_flags = 0;
 
 	trace_xfs_setattr(ip);
@@ -720,10 +720,10 @@ xfs_setattr_size(
 			ATTR_MTIME_SET|ATTR_KILL_SUID|ATTR_KILL_SGID|
 			ATTR_KILL_PRIV|ATTR_TIMES_SET)) == 0);
 
-	lock_flags = XFS_ILOCK_EXCL;
-	if (!(flags & XFS_ATTR_NOLOCK))
+	if (!(flags & XFS_ATTR_NOLOCK)) {
 		lock_flags |= XFS_IOLOCK_EXCL;
 		xfs_ilock(ip, lock_flags);
+	}
 
 	oldsize = inode->i_size;
 	newsize = iattr->ia_size;
@@ -746,7 +746,7 @@ xfs_setattr_size(
 	/*
 	 * Make sure that the dquots are attached to the inode.
 	 */
-	error = xfs_qm_dqattach_locked(ip, 0);
+	error = xfs_qm_dqattach(ip, 0);
 	if (error)
 		goto out_unlock;
 
@@ -764,12 +764,12 @@ xfs_setattr_size(
 		 * before the inode is joined to the transaction to modify
 		 * i_size.
 		 */
+		xfs_ilock(ip, XFS_ILOCK_EXCL);
 		error = xfs_zero_eof(ip, newsize, oldsize);
+		xfs_iunlock(ip, XFS_ILOCK_EXCL);
 		if (error)
 			goto out_unlock;
 	}
-	xfs_iunlock(ip, XFS_ILOCK_EXCL);
-	lock_flags &= ~XFS_ILOCK_EXCL;
 
 	/*
 	 * We are going to log the inode size change in this transaction so