xfs: assorted fixes for 5.14, part 1

This branch contains the first round of various small fixes for 5.14.
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Merge tag 'assorted-fixes-5.14-1_2021-06-03' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux into xfs-5.14-merge2

xfs: assorted fixes for 5.14, part 1

This branch contains the first round of various small fixes for 5.14.

* tag 'assorted-fixes-5.14-1_2021-06-03' of https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux:
  xfs: don't take a spinlock unconditionally in the DIO fastpath
  xfs: mark xfs_bmap_set_attrforkoff static
  xfs: Remove redundant assignment to busy
  xfs: sort variable alphabetically to avoid repeated declaration

fs/xfs/libxfs/xfs_alloc.c

@@ -1676,7 +1676,6 @@ restart:
 	cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, args->agbp,
 					args->pag, XFS_BTNUM_CNT);
 	bno_cur = NULL;
-	busy = false;
 
 	/*
 	 * Look for an entry >= maxlen+alignment-1 blocks.

fs/xfs/libxfs/xfs_bmap.c

@@ -1029,7 +1029,7 @@ xfs_bmap_add_attrfork_local(
 /*
  * Set an inode attr fork offset based on the format of the data fork.
  */
-int
+static int
 xfs_bmap_set_attrforkoff(
 	struct xfs_inode	*ip,
 	int			size,

fs/xfs/libxfs/xfs_bmap.h

@@ -187,7 +187,6 @@ void	xfs_trim_extent(struct xfs_bmbt_irec *irec, xfs_fileoff_t bno,
 		xfs_filblks_t len);
 unsigned int xfs_bmap_compute_attr_offset(struct xfs_mount *mp);
 int	xfs_bmap_add_attrfork(struct xfs_inode *ip, int size, int rsvd);
-int	xfs_bmap_set_attrforkoff(struct xfs_inode *ip, int size, int *version);
 void	xfs_bmap_local_to_extents_empty(struct xfs_trans *tp,
 		struct xfs_inode *ip, int whichfork);
 void	__xfs_bmap_add_free(struct xfs_trans *tp, xfs_fsblock_t bno,

fs/xfs/libxfs/xfs_shared.h

@@ -22,30 +22,26 @@ struct xfs_inode;
  * Buffer verifier operations are widely used, including userspace tools
  */
 extern const struct xfs_buf_ops xfs_agf_buf_ops;
-extern const struct xfs_buf_ops xfs_agi_buf_ops;
-extern const struct xfs_buf_ops xfs_agf_buf_ops;
 extern const struct xfs_buf_ops xfs_agfl_buf_ops;
-extern const struct xfs_buf_ops xfs_bnobt_buf_ops;
-extern const struct xfs_buf_ops xfs_cntbt_buf_ops;
-extern const struct xfs_buf_ops xfs_rmapbt_buf_ops;
-extern const struct xfs_buf_ops xfs_refcountbt_buf_ops;
+extern const struct xfs_buf_ops xfs_agi_buf_ops;
 extern const struct xfs_buf_ops xfs_attr3_leaf_buf_ops;
 extern const struct xfs_buf_ops xfs_attr3_rmt_buf_ops;
 extern const struct xfs_buf_ops xfs_bmbt_buf_ops;
+extern const struct xfs_buf_ops xfs_bnobt_buf_ops;
+extern const struct xfs_buf_ops xfs_cntbt_buf_ops;
 extern const struct xfs_buf_ops xfs_da3_node_buf_ops;
 extern const struct xfs_buf_ops xfs_dquot_buf_ops;
-extern const struct xfs_buf_ops xfs_symlink_buf_ops;
-extern const struct xfs_buf_ops xfs_agi_buf_ops;
-extern const struct xfs_buf_ops xfs_inobt_buf_ops;
+extern const struct xfs_buf_ops xfs_dquot_buf_ra_ops;
 extern const struct xfs_buf_ops xfs_finobt_buf_ops;
+extern const struct xfs_buf_ops xfs_inobt_buf_ops;
 extern const struct xfs_buf_ops xfs_inode_buf_ops;
 extern const struct xfs_buf_ops xfs_inode_buf_ra_ops;
-extern const struct xfs_buf_ops xfs_dquot_buf_ops;
-extern const struct xfs_buf_ops xfs_dquot_buf_ra_ops;
+extern const struct xfs_buf_ops xfs_refcountbt_buf_ops;
+extern const struct xfs_buf_ops xfs_rmapbt_buf_ops;
+extern const struct xfs_buf_ops xfs_rtbuf_ops;
 extern const struct xfs_buf_ops xfs_sb_buf_ops;
 extern const struct xfs_buf_ops xfs_sb_quiet_buf_ops;
 extern const struct xfs_buf_ops xfs_symlink_buf_ops;
-extern const struct xfs_buf_ops xfs_rtbuf_ops;
 
 /* log size calculation functions */
 int	xfs_log_calc_unit_res(struct xfs_mount *mp, int unit_bytes);

fs/xfs/xfs_file.c

@@ -384,21 +384,30 @@ restart:
 		}
 		goto restart;
 	}
+
 	/*
 	 * If the offset is beyond the size of the file, we need to zero any
 	 * blocks that fall between the existing EOF and the start of this
-	 * write.  If zeroing is needed and we are currently holding the
-	 * iolock shared, we need to update it to exclusive which implies
-	 * having to redo all checks before.
+	 * write.  If zeroing is needed and we are currently holding the iolock
+	 * shared, we need to update it to exclusive which implies having to
+	 * redo all checks before.
 	 *
-	 * We need to serialise against EOF updates that occur in IO
-	 * completions here. We want to make sure that nobody is changing the
-	 * size while we do this check until we have placed an IO barrier (i.e.
-	 * hold the XFS_IOLOCK_EXCL) that prevents new IO from being dispatched.
-	 * The spinlock effectively forms a memory barrier once we have the
-	 * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value
-	 * and hence be able to correctly determine if we need to run zeroing.
+	 * We need to serialise against EOF updates that occur in IO completions
+	 * here. We want to make sure that nobody is changing the size while we
+	 * do this check until we have placed an IO barrier (i.e.  hold the
+	 * XFS_IOLOCK_EXCL) that prevents new IO from being dispatched.  The
+	 * spinlock effectively forms a memory barrier once we have the
+	 * XFS_IOLOCK_EXCL so we are guaranteed to see the latest EOF value and
+	 * hence be able to correctly determine if we need to run zeroing.
+	 *
+	 * We can do an unlocked check here safely as IO completion can only
+	 * extend EOF. Truncate is locked out at this point, so the EOF can
+	 * not move backwards, only forwards. Hence we only need to take the
+	 * slow path and spin locks when we are at or beyond the current EOF.
 	 */
+	if (iocb->ki_pos <= i_size_read(inode))
+		goto out;
+
 	spin_lock(&ip->i_flags_lock);
 	isize = i_size_read(inode);
 	if (iocb->ki_pos > isize) {
@@ -426,7 +435,7 @@ restart:
 			drained_dio = true;
 			goto restart;
 		}
-	
+
 		trace_xfs_zero_eof(ip, isize, iocb->ki_pos - isize);
 		error = iomap_zero_range(inode, isize, iocb->ki_pos - isize,
 				NULL, &xfs_buffered_write_iomap_ops);
@@ -435,6 +444,7 @@ restart:
 	} else
 		spin_unlock(&ip->i_flags_lock);
 
+out:
 	return file_modified(file);
 }
 
@@ -500,7 +510,17 @@ xfs_dio_write_end_io(
 	 * other IO completions here to update the EOF. Failing to serialise
 	 * here can result in EOF moving backwards and Bad Things Happen when
 	 * that occurs.
+	 *
+	 * As IO completion only ever extends EOF, we can do an unlocked check
+	 * here to avoid taking the spinlock. If we land within the current EOF,
+	 * then we do not need to do an extending update at all, and we don't
+	 * need to take the lock to check this. If we race with an update moving
+	 * EOF, then we'll either still be beyond EOF and need to take the lock,
+	 * or we'll be within EOF and we don't need to take it at all.
 	 */
+	if (offset + size <= i_size_read(inode))
+		goto out;
+
 	spin_lock(&ip->i_flags_lock);
 	if (offset + size > i_size_read(inode)) {
 		i_size_write(inode, offset + size);