linux-kernel - Re: [PATCH v4 0/5] cpumask: Fix invalid uniprocessor assumptions

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Message-ID: <f58ee2c553ea8ae991454a8e195dcbd2821f794c.camel@svanheule.net>
Date:   Sun, 10 Jul 2022 08:51:08 +0200
From:   Sander Vanheule <sander@...nheule.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        elver@...gle.com, gregkh@...uxfoundation.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, vschneid@...hat.com,
        Yury Norov <yury.norov@...il.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v4 0/5] cpumask: Fix invalid uniprocessor assumptions

Hi Andrew,

On Sun, 2022-07-03 at 13:39 -0700, Andrew Morton wrote:
> On Sun, 03 Jul 2022 09:50:51 +0200 Sander Vanheule <sander@...nheule.net>
> wrote:
> 
> > On Sat, 2022-07-02 at 13:38 -0700, Andrew Morton wrote:
> > > On Sat,  2 Jul 2022 18:08:23 +0200 Sander Vanheule <sander@...nheule.net>
> > > wrote:
> > > 
> > > > On uniprocessor builds, it is currently assumed that any cpumask will
> > > > contain the single CPU: cpu0. This assumption is used to provide
> > > > optimised implementations.
> > > > 
> > > > The current assumption also appears to be wrong, by ignoring the fact
> > > > that users can provide empty cpumask-s. This can result in bugs as
> > > > explained in [1].
> > > 
> > > It's a little unkind to send people off to some link to explain the
> > > very core issue which this patchset addresses!  So I enhanced this
> > > paragraph:
> > > 
> > > : The current assumption also appears to be wrong, by ignoring the fact
> > > that
> > > : users can provide empty cpumasks.  This can result in bugs as explained
> > > in
> > > : [1] - for_each_cpu() will run one iteration of the loop even when passed
> > > : an empty cpumask.
> > 
> > Makes sense to add this, sorry for the inconvenience.
> > 
> > Just to make sure, since I'm not familiar with the process for patches going
> > through the mm tree,
> 
> Patches enter -mm in quilt form and are published in the (rebasing)
> mm-unstable branch
> git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.  Once they have
> stopped changing and have been stabilized, I move them into the
> non-rebasing mm-stable branch.
> 
> > can I still send a v5 to move the last patch forward in the series, and to
> > include Yury's tags?
> 
> I already added Yury's ack.  Please tell me the specific patch ordering
> and I'll take care of that.
> 

The updated patch order should be:
   x86/cacheinfo: move shared cache map definitions
   cpumask: add UP optimised for_each_*_cpu versions
   cpumask: fix invalid uniprocessor mask assumption
   lib/test: introduce cpumask KUnit test suite
   cpumask: update cpumask_next_wrap() signature

Reordering the patches on my tree didn't produce any conflicts.

Best,
Sander