[PATCH] Re: [PATCH] VFS readahead bug in 2.6.8-rc[1-3]

[Ram Pai <linuxram@us.ibm.com>]

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On Fri, 6 Aug 2004, Andrew Morton wrote:

> Phillip Lougher <phillip@lougher.demon.co.uk> wrote:
> >
> > Nick Piggin wrote:
> > 
> > > No, I suggest you start to code assuming this interface does
> > > what it does. I didn't say there is no bug here, but nobody
> > > else's filesystem breaks.
> > > 
> > 
> > To stop this silly argument from escalating, I will patch my code.
> > 
> 
> Well I don't think it's silly.
> 
> We are deterministically asking the fs to read a page which lies outside
> EOF, and we shouldn't.  If for no other reason than that the ever-popular
> "read a million 4k files" workload will consume extra CPU and twice the
> pagecache.

Andrew,

	Enclosed a patch developed with Nick Piggin. It takes care of the
	bug. 

Thanks,
RP

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--- ram/linux-2.6.8.1/mm/filemap.c	2004-08-14 03:56:25.000000000 -0700
+++ linux-2.6.8.1/mm/filemap.c	2004-08-16 07:56:31.912038720 -0700
@@ -665,14 +665,18 @@ void do_generic_mapping_read(struct addr
 	offset = *ppos & ~PAGE_CACHE_MASK;
 
 	isize = i_size_read(inode);
-	end_index = isize >> PAGE_CACHE_SHIFT;
-	if (index > end_index)
+	if (!isize)
 		goto out;
+		
+	end_index = isize >> PAGE_CACHE_SHIFT;
 
 	for (;;) {
 		struct page *page;
 		unsigned long nr, ret;
 
+		if (index > end_index)
+			goto out;
+
 		cond_resched();
 		page_cache_readahead(mapping, &ra, filp, index);