On 06/20/16 at 03:17P, Al Viro wrote:
> On Mon, Jun 20, 2016 at 10:05:45PM +0800, Minfei Huang wrote:
> > Ping. Any comment is appreciate.
> >
> > Thanks
> > Minfei
> >
> > On 06/13/16 at 12:33P, Minfei Huang wrote:
> > > The variable nr_pages is always more than 1, because the size of
> > > structure aio_ring is bigger than 0. So remove unnecessary test for
> > > nr_page.
>
> What this test really checks is that the value we'd put into nr_pages
> (PFN_UP(size)) is not greater than 2^31. Whether it's redundant or not
> is a separate question - it very well might be, due to the code in
> ioctx_alloc() that caps nr_events, but that needs a proof. In any case,
> the reasons you are offering in commit message are wrong - it's about
> size being too _large_, not too small.
Hmm. But there is a following test in function ioctx_alloc which is used
to limit the max of nr_events.
713 /* Prevent overflows */
714 if (nr_events > (0x10000000U / sizeof(struct io_event))) {
715 pr_debug("ENOMEM: nr_events too high\n");
716 return ERR_PTR(-EINVAL);
717 }
So according to this test, we can make sure that nr_pages(PFN_UP(size))
cann't be greater than 2^31, and max to 2^28.
Thanks
Minfei
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