Re: [PATCH v1 3/5] treewide: use get_random_u32() when possible

Andy Shevchenko
2022-10-06T13:20:59Z

On Thu, Oct 06, 2022 at 07:05:48AM -0600, Jason A. Donenfeld wrote:
> On Thu, Oct 6, 2022 at 6:47 AM Jason Gunthorpe <jgg@ziepe.ca> wrote:
> > On Wed, Oct 05, 2022 at 11:48:42PM +0200, Jason A. Donenfeld wrote:

...

> > > - u32 isn = (prandom_u32() & ~7UL) - 1;
> > > + u32 isn = (get_random_u32() & ~7UL) - 1;
> >
> > Maybe this wants to be written as
> >
> > (prandom_max(U32_MAX >> 7) << 7) | 7

> > ?
>
> Holy smokes. Yea I guess maybe? It doesn't exactly gain anything or
> make the code clearer though, and is a little bit more magical than
> I'd like on a first pass.

Shouldn't the two first 7s to be 3s?

...

> > > - psn = prandom_u32() & 0xffffff;
> > > + psn = get_random_u32() & 0xffffff;
> >
> > prandom_max(0xffffff + 1)
>
> That'd work, but again it's not more clear. Authors here are going for
> a 24-bit number, and masking seems like a clear way to express that.

We have some 24-bit APIs (and 48-bit) already in kernel, why not to have
get_random_u24() ?

--
With Best Regards,
Andy Shevchenko