During umount we do not add a dirty inode to the lru and wait for it to
become clean first, but force writeback of data and metadata with
I_WILL_FREE set.  Currently there is no way for XFS to detect that the
inode has been redirtied for metadata operations, as we skip the
mark_inode_dirty call during teardown.  Fix this by setting i_update_core
nanually in that case, so that the inode gets flushed during inode reclaim.

Alternatively we could enable calling mark_inode_dirty for inodes in
I_WILL_FREE state, and let the VFS dirty tracking handle this.  I decided
against this as we will get better I/O patterns from reclaim compared to
the synchronous writeout in write_inode_now, and always marking the inode
dirty in some way from xfs_mark_inode_dirty is a better safetly net in
either case.

Signed-off-by: Christoph Hellwig <hch@lst.de>

Index: linux-2.6/fs/xfs/xfs_iops.c
===================================================================

--- linux-2.6.orig/fs/xfs/xfs_iops.c	2011-08-26 12:31:19.090631739 +0200
+++ linux-2.6/fs/xfs/xfs_iops.c	2011-08-26 12:35:43.692531800 +0200

@@ -70,9 +70,8 @@ xfs_synchronize_times(
 }
 
 /*
- * If the linux inode is valid, mark it dirty.
- * Used when committing a dirty inode into a transaction so that
- * the inode will get written back by the linux code
+ * If the linux inode is valid, mark it dirty, else mark the dirty state
+ * in the XFS inode to make sure we pick it up when reclaiming the inode.
  */
 void
 xfs_mark_inode_dirty_sync(

@@ -82,6 +81,10 @@ xfs_mark_inode_dirty_sync(
 
 	if (!(inode->i_state & (I_WILL_FREE|I_FREEING)))
 		mark_inode_dirty_sync(inode);
+	else {
+		barrier();
+		ip->i_update_core = 1;
+	}
 }