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SubjectRe: [PATCH] VFS readahead bug in 2.6.8-rc[1-3]
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On Thu, 2004-08-05 at 23:19, Nick Piggin wrote:
> Ram Pai wrote:
>
> >
> > there is a check in __do_page_cache_readahead() that validates this.
> > But it is still not guaranteed to work correctly against races.
> >
> > The filesystem has to handle such out-of-bound requests gracefully.
> >
> > However with Nick's fix in do_generic_mapping_read() the filesystem
> > is gauranteed to be called with out-of-bound index, if the file size
> > is a multiple of 4k. Without the fix, the filesystem might get
> > called with out-of-bound index only in racy conditions.
> >
>
> How's this?

If I understand your patch correctly: it takes care of files whose size
is 0 bytes, but not files of size 4k bytes or 8k bytes. or .. n*4k bytes

I think the original check that you removed should be reverted back and
the additional check that you introduced should remain.

RP
>
> ---
>
> linux-2.6-npiggin/mm/filemap.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff -puN mm/filemap.c~fs-fix mm/filemap.c
> --- linux-2.6/mm/filemap.c~fs-fix 2004-08-06 16:16:26.000000000 +1000
> +++ linux-2.6-npiggin/mm/filemap.c 2004-08-06 16:18:22.000000000 +1000
> @@ -716,9 +716,9 @@ 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 (*ppos >= isize)
> goto out;
> + end_index = isize >> PAGE_CACHE_SHIFT;
>
> for (;;) {
> struct page *page;
>
> _

-
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