Commit 84209e02 authored Aug 01, 2008 by Miklos Szeredi Committed by Linus Torvalds Aug 02, 2008

mm: dont clear PG_uptodate on truncate/invalidate



Brian Wang reported that a FUSE filesystem exported through NFS could
return I/O errors on read.  This was traced to splice_direct_to_actor()
returning a short or zero count when racing with page invalidation.

However this is not FUSE or NFSD specific, other filesystems (notably
NFS) also call invalidate_inode_pages2() to purge stale data from the
cache.

If this happens while such pages are sitting in a pipe buffer, then
splice(2) from the pipe can return zero, and read(2) from the pipe can
return ENODATA.

The zero return is especially bad, since it implies end-of-file or
disconnected pipe/socket, and is documented as such for splice.  But
returning an error for read() is also nasty, when in fact there was no
error (data becoming stale is not an error).

The same problems can be triggered by "hole punching" with
madvise(MADV_REMOVE).

Fix this by not clearing the PG_uptodate flag on truncation and
invalidation.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2b12a4c5

mm/truncate.c

+0 −2

Original line number	Original line	Diff line number	Diff line
	@@ -104,7 +104,6 @@ truncate_complete_page(struct address_space mapping, struct page page)
	cancel_dirty_page(page, PAGE_CACHE_SIZE);		cancel_dirty_page(page, PAGE_CACHE_SIZE);

	remove_from_page_cache(page);		remove_from_page_cache(page);
	ClearPageUptodate(page);
	ClearPageMappedToDisk(page);		ClearPageMappedToDisk(page);
	page_cache_release(page); /* pagecache ref */		page_cache_release(page); /* pagecache ref */
	}		}
	@@ -356,7 +355,6 @@ invalidate_complete_page2(struct address_space mapping, struct page page)
	BUG_ON(PagePrivate(page));		BUG_ON(PagePrivate(page));
	__remove_from_page_cache(page);		__remove_from_page_cache(page);
	spin_unlock_irq(&mapping->tree_lock);		spin_unlock_irq(&mapping->tree_lock);
	ClearPageUptodate(page);
	page_cache_release(page); /* pagecache ref */		page_cache_release(page); /* pagecache ref */
	return 1;		return 1;
	failed:		failed:

Admin message