[PATCH 05/14] xfs: reorder zeroing and flushing sequence in truncate

[Christoph Hellwig <hch@xxxxxx>]

Currently zeroing out blocks and waiting for writeout is a bit of a mess in
truncate.  This patch gives it a clear order in preparation for the iomap
path:

 (1) we first wait for any direct I/O to complete to prevent any races
     for it
 (2) we then perform the actual zeroing, and only use the truncate_page
     helpers for truncating down.  The truncate up case already is
     handled by the separate call to xfs_zero_eof.
 (3) only then we write back dirty data, as zeroing block may cause
     dirty pages when using either xfs_zero_eof or the new iomap
     infrastructure.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Bob Peterson <rpeterso@xxxxxxxxxx>
---
 fs/xfs/xfs_iops.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index c5d4eba..1a5ca4b 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -801,20 +801,35 @@ xfs_setattr_size(
                return error;
 
        /*
+        * Wait for all direct I/O to complete.
+        */
+       inode_dio_wait(inode);
+
+       /*
         * File data changes must be complete before we start the transaction to
         * modify the inode.  This needs to be done before joining the inode to
         * the transaction because the inode cannot be unlocked once it is a
         * part of the transaction.
         *
-        * Start with zeroing any data block beyond EOF that we may expose on
-        * file extension.
+        * Start with zeroing any data beyond EOF that we may expose on file
+        * extension, or zeroing out the rest of the block on a downward
+        * truncate.
         */
        if (newsize > oldsize) {
                error = xfs_zero_eof(ip, newsize, oldsize, &did_zeroing);
-               if (error)
-                       return error;
+       } else {
+               if (IS_DAX(inode)) {
+                       error = dax_truncate_page(inode, newsize,
+                                       xfs_get_blocks_direct);
+               } else {
+                       error = block_truncate_page(inode->i_mapping, newsize,
+                                       xfs_get_blocks);
+               }
        }
 
+       if (error)
+               return error;
+
        /*
         * We are going to log the inode size change in this transaction so
         * any previous writes that are beyond the on disk EOF and the new
@@ -831,9 +846,6 @@ xfs_setattr_size(
                        return error;
        }
 
-       /* Now wait for all direct I/O to complete. */
-       inode_dio_wait(inode);
-
        /*
         * We've already locked out new page faults, so now we can safely remove
         * pages from the page cache knowing they won't get refaulted until we
@@ -851,13 +863,6 @@ xfs_setattr_size(
         * to hope that the caller sees ENOMEM and retries the truncate
         * operation.
         */
-       if (IS_DAX(inode))
-               error = dax_truncate_page(inode, newsize, 
xfs_get_blocks_direct);
-       else
-               error = block_truncate_page(inode->i_mapping, newsize,
-                                           xfs_get_blocks);
-       if (error)
-               return error;
        truncate_setsize(inode, newsize);
 
        error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
-- 
2.1.4