[patch 1/2] mm: dont clear PG_uptodate in invalidate_complete_page2()

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

Clearing the uptodate page flag will cause page_cache_pipe_buf_confirm()
to return -ENODATA if that page was in the buffer.  This in turn will cause
splice() to return a short or zero count.

This manifested itself in rare I/O errors seen on nfs exported fuse
filesystems.  This is because nfsd uses splice_direct_to_actor() to
read files, and fuse uses invalidate_inode_pages2() to invalidate
stale data on open.

Fix this by not clearing PG_uptodate on page invalidation.  This will
result in the old, invalid page contents being copied.  But that's OK,
the contents were valid at splice-in time (which is when the the
"copy" was conceptually done).

I haven't done an audit of all code that checks the PG_uptodate flags,
but I suspect, that this change won't have any harmful effects.  Most
code checks page->mapping to see if the page was truncated or
invalidated, before using it, and retries the find/read on the page if
it wasn't.  The page_cache_pipe_buf_confirm() code is an exception in
this regard.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 mm/truncate.c |    1 -
 1 file changed, 1 deletion(-)

Index: linux-2.6/mm/truncate.c
===================================================================
--- linux-2.6.orig/mm/truncate.c	2008-06-24 20:49:25.000000000 +0200
+++ linux-2.6/mm/truncate.c	2008-06-24 23:28:32.000000000 +0200
@@ -356,7 +356,6 @@ invalidate_complete_page2(struct address
 	BUG_ON(PagePrivate(page));
 	__remove_from_page_cache(page);
 	write_unlock_irq(&mapping->tree_lock);
-	ClearPageUptodate(page);
 	page_cache_release(page);	/* pagecache ref */
 	return 1;
 failed:

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