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

[Phillip Lougher]

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?

It doesn't work.  It correctly handles the case where *ppos is equal
to i_size on entry to the function (and this does work for files 0, 4k
and n * 4k in length), but it doesn't handle readahead inside the for
loop.  The check needs to be in the for loop.

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