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SubjectRe: [PATCH] mm: readahead: fix do_readahead for no readpage(s)
On Tue, 28 Jan 2014 23:01:26 +0200 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:

> On Tue, Jan 28, 2014 at 12:03:01PM -0800, Andrew Morton wrote:
> > On Tue, 28 Jan 2014 11:14:19 +0000 Mark Rutland <mark.rutland@arm.com> wrote:
> >
> > > Commit 63d0f0a3c7e1 (mm/readahead.c:do_readhead(): don't check for
> > > ->readpage) unintentionally made do_readahead return 0 for all valid
> > > files regardless of whether readahead was supported, rather than the
> > > expected -EINVAL. This gets forwarded on to userspace, and results in
> > > sys_readahead appearing to succeed in cases that don't make sense (e.g.
> > > when called on pipes or sockets). This issue is detected by the LTP
> > > readahead01 testcase.
> >
> > How can this be?
> >
> > : static ssize_t
> > : do_readahead(struct address_space *mapping, struct file *filp,
> > : pgoff_t index, unsigned long nr)
> > : {
> > : if (!mapping || !mapping->a_ops)
> > : return -EINVAL;
> > :
> > : return force_page_cache_readahead(mapping, filp, index, nr);
>
> It's not what we have in Linus' tree. force_page_cache_readahead() return
> code is unused:
>
> force_page_cache_readahead(mapping, filp, index, nr);
> return 0;
>

ah, oops, I was looking at the code with Mark's patch applied.

Yes, the force_page_cache_readahead() return value should be propagated.

And I guess the lobotomising of the force_page_cache_readahead() return
value is OK. force_page_cache_readahead() presently returns an errno
even if it has performed some reads. A read()-style function shouldn't
do that - it should return a short read in that case.



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