linux-kernel - Re: [PATCH RFC cpumask] Allow "all", "none", and "last" in cpumask strings

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Date:   Wed, 20 Jan 2021 23:11:48 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     paulmck@...nel.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        kernel-team@...com, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH RFC cpumask] Allow "all", "none", and "last" in cpumask strings

On Wed, Jan 6, 2021 at 12:49 AM Yury Norov <yury.norov@...il.com> wrote:
>
> On Tue, Jan 5, 2021 at 4:48 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > Hello!
> >
> > This series allows "all", "none", and "last" to be used in cpumask
> > strings.  This allows these strings to be less dependent on the underlying
> > system.  For example, currently a string specifying all but the first
> > CPU must be "1-7" on an eight-CPU system and "1-15" on a 16-CPU system.
> > With this series, the single string "1-last" can be used regardless of the
> > number of CPUs (at least assuming that each system has at least one CPU).
>
> 'none' may be implemented as an empty string or string with separators only,
> but I have nothing against explicit 'none'. See other comments inline.
>
> Thanks,
> Yury.
>
> > 1.      Un-inline cpulist_parse for SMP; prepare for ascii helpers,
> >         courtesy of Paul Gortmaker.
> >
> > 2.      Make "all" alias global and not just RCU, courtesy of Paul
> >         Gortmaker.
> >
> > 3.      Add a "none" alias to complement "all", courtesy of Paul
> >         Gortmaker.
> >
> > 4.      Add "last" alias for cpu list specifications, courtesy of Paul
> >         Gortmaker.
> >
> > 5.      Use "all" and "last" in "nohz_full" and "rcu_nocbs".
> >
> >                                                 Thanx, Paul

Hi Paul,

Today I found this series in linux-next despite downsides discovered during
the review. This series introduces absolutely unneeded cap on the number of
cpus in the system (9999), and also adds unsafe and non-optimal code.

In addition to that, I observe this warning on powerpc:
  CC      lib/cpumask.o
lib/cpumask.c: In function ‘cpulist_parse’:
lib/cpumask.c:222:17: warning: cast from pointer to integer of
different size [-Wpointer-to-int-cast]
  222 |   memblock_free((phys_addr_t)cpulist, len);
      |                 ^

Can you please revert this series unless all the problems will be fixed?

Thanks,
Yury