[PATCH] xfs: do not discard page cache data on EAGAIN

[Christoph Hellwig]

If xfs_map_blocks returns EAGAIN because of lock contention we must redirty
the page and not disard the pagecache content and return an error from
writepage.  We used to do this correctly, but the logic got lost during
the recent reshuffle of the writepage code.

Signed-off-by: Christoph Hellwig <hch at lst.de>
Reported-by: Mike Gao <ygao.linux at gmail.com> 
Tested-by: Mike Gao <ygao.linux at gmail.com> 

Index: xfs/fs/xfs/linux-2.6/xfs_aops.c
===================================================================
--- xfs.orig/fs/xfs/linux-2.6/xfs_aops.c	2010-08-18 18:10:48.140261091 +0200
+++ xfs/fs/xfs/linux-2.6/xfs_aops.c	2010-08-18 18:12:41.167005888 +0200
@@ -1068,7 +1068,7 @@ xfs_vm_writepage(
 	 * by themselves.
 	 */
 	if ((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == PF_MEMALLOC)
-		goto out_fail;
+		goto redirty;
 
 	/*
 	 * We need a transaction if there are delalloc or unwritten buffers
@@ -1080,7 +1080,7 @@ xfs_vm_writepage(
 	 */
 	xfs_count_page_state(page, &delalloc, &unwritten);
 	if ((current->flags & PF_FSTRANS) && (delalloc || unwritten))
-		goto out_fail;
+		goto redirty;
 
 	/* Is this page beyond the end of the file? */
 	offset = i_size_read(inode);
@@ -1245,12 +1245,15 @@ error:
 	if (iohead)
 		xfs_cancel_ioend(iohead);
 
+	if (err == -EAGAIN)
+		goto redirty;
+
 	xfs_aops_discard_page(page);
 	ClearPageUptodate(page);
 	unlock_page(page);
 	return err;
 
-out_fail:
+redirty:
 	redirty_page_for_writepage(wbc, page);
 	unlock_page(page);
 	return 0;