diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index c02a47453137..598b259fda04 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1582,9 +1582,16 @@ xfs_end_io_direct_write(
 	 * with the on-disk inode size being outside the in-core inode size. We
 	 * have no other method of updating EOF for AIO, so always do it here
 	 * if necessary.
+	 *
+	 * We need to lock the test/set EOF update as we can be racing with
+	 * 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.
 	 */
+	spin_lock(&ip->i_flags_lock);
 	if (offset + size > i_size_read(inode))
 		i_size_write(inode, offset + size);
+	spin_unlock(&ip->i_flags_lock);
 
 	/*
 	 * If we are doing an append IO that needs to update the EOF on disk,
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index ce615d12fb44..2323b8b63183 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -565,8 +565,18 @@ restart:
 	 * 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.
 	 */
+	spin_lock(&ip->i_flags_lock);
 	if (*pos > i_size_read(inode)) {
+		spin_unlock(&ip->i_flags_lock);
 		if (*iolock == XFS_IOLOCK_SHARED) {
 			xfs_rw_iunlock(ip, *iolock);
 			*iolock = XFS_IOLOCK_EXCL;
@@ -576,7 +586,8 @@ restart:
 		error = xfs_zero_eof(ip, *pos, i_size_read(inode));
 		if (error)
 			return error;
-	}
+	} else
+		spin_unlock(&ip->i_flags_lock);
 
 	/*
 	 * Updating the timestamps will grab the ilock again from