Date:   Mon, 6 Mar 2023 08:54:06 -0800
From:   Yury Norov <yury.norov@gmail.com>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Vernon Yang <vernon2gm@gmail.com>, torvalds@linux-foundation.org,
        tytso@mit.edu, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, pabeni@redhat.com, jejb@linux.ibm.com,
        martin.petersen@oracle.com, andriy.shevchenko@linux.intel.com,
        linux@rasmusvillemoes.dk, james.smart@broadcom.com,
        dick.kennedy@broadcom.com, linux-kernel@vger.kernel.org,
        wireguard@lists.zx2c4.com, netdev@vger.kernel.org,
        linux-scsi@vger.kernel.org
Subject: Re: [PATCH 5/5] cpumask: fix comment of cpumask_xxx
Message-ID: <ZAYartD+NsF1JxlH@yury-laptop>
References: <20230306160651.2016767-1-vernon2gm@gmail.com>
 <20230306160651.2016767-6-vernon2gm@gmail.com>
 <ZAYXJ2E+JHcp2kD/@yury-laptop>
 <CAHmME9r_JXNCVVCNxZRQkafA=eOOu5k0+AweRDor3tNu283bdg@mail.gmail.com>
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On Mon, Mar 06, 2023 at 05:44:41PM +0100, Jason A. Donenfeld wrote:
> On Mon, Mar 6, 2023 at 5:39 PM Yury Norov <yury.norov@gmail.com> wrote:
> >
> > On Tue, Mar 07, 2023 at 12:06:51AM +0800, Vernon Yang wrote:
> > > After commit 596ff4a09b89 ("cpumask: re-introduce constant-sized cpumask
> > > optimizations"), the cpumask size is divided into three different case,
> > > so fix comment of cpumask_xxx correctly.
> > >
> > > Signed-off-by: Vernon Yang <vernon2gm@gmail.com>
> > > ---
> > >  include/linux/cpumask.h | 46 ++++++++++++++++++++---------------------
> > >  1 file changed, 23 insertions(+), 23 deletions(-)
> > >
> > > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
> > > index 8fbe76607965..248bdb1c50dc 100644
> > > --- a/include/linux/cpumask.h
> > > +++ b/include/linux/cpumask.h
> > > @@ -155,7 +155,7 @@ static __always_inline unsigned int cpumask_check(unsigned int cpu)
> > >   * cpumask_first - get the first cpu in a cpumask
> > >   * @srcp: the cpumask pointer
> > >   *
> > > - * Returns >= nr_cpu_ids if no cpus set.
> > > + * Returns >= small_cpumask_bits if no cpus set.
> >
> > There's no such thing like small_cpumask_bits. Here and everywhere,
> > nr_cpu_ids must be used.
> >
> > Actually, before 596ff4a09b89 nr_cpumask_bits was deprecated, and it
> > must be like that for all users even now.
> >
> > nr_cpumask_bits must be considered as internal cpumask parameter and
> > never referenced outside of cpumask code.
> 
> What's the right thing I should do, then, for wireguard's usage and
> for random.c's usage? It sounds like you object to this patchset, but
> if the problem is real, it sounds like I should at least fix the two
> cases I maintain. What's the right check?

Everywhere outside of cpumasks internals use (cpu < nr_cpu_ids) to
check if the cpu is in a valid range, like:

cpu = cpumask_first(cpus);
if (cpu >= nr_cpu_ids)
        pr_err("There's no cpus");