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Date:   Thu, 6 Oct 2022 07:07:24 -0600
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Jan Kara <jack@...e.cz>, Andrew Lunn <andrew@...n.ch>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
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        Andrii Nakryiko <andrii@...nel.org>,
        Hans Verkuil <hverkuil@...all.nl>, linux-sctp@...r.kernel.org,
        "Md . Haris Iqbal" <haris.iqbal@...os.com>,
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        Rohit Maheshwari <rohitm@...lsio.com>,
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        Martin KaFai Lau <martin.lau@...ux.dev>
Subject: Re: [f2fs-dev] [PATCH v1 3/5] treewide: use get_random_u32() when possible

On Thu, Oct 6, 2022 at 7:01 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Oct 06, 2022 at 06:33:15AM -0600, Jason A. Donenfeld wrote:
> > On Thu, Oct 06, 2022 at 10:43:31AM +0200, Jan Kara wrote:
>
> ...
>
> > > The code here is effectively doing the
> > >
> > >     parent_group = prandom_u32_max(ngroups);
> > >
> > > Similarly here we can use prandom_u32_max(ngroups) like:
> > >
> > >             if (qstr) {
> > >                     ...
> > >                     parent_group = hinfo.hash % ngroups;
> > >             } else
> > >                     parent_group = prandom_u32_max(ngroups);
> >
> > Nice catch. I'll move these to patch #1.
>
> I believe coccinelle is able to handle this kind of code as well

I'd be extremely surprised. The details were kind of non obvious. I
just spent a decent amount of time manually checking those blocks, to
make sure we didn't wind up with different behavior, given the
variable reuse.

Jason

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