linux-kernel - RE: [PATCH 1/9] tools: convert cgroup_sel.refcnt from atomic_t to refcount

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Date:   Wed, 22 Feb 2017 16:10:59 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "jolsa@...nel.org" <jolsa@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "matija.glavinic-pecotic.ext@...ia.com" 
        <matija.glavinic-pecotic.ext@...ia.com>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: RE: [PATCH 1/9] tools: convert cgroup_sel.refcnt from atomic_t to
 refcount_t

> Em Wed, Feb 22, 2017 at 02:29:18PM +0000, Reshetova, Elena escreveu:
> > > Em Tue, Feb 21, 2017 at 05:34:55PM +0200, Elena Reshetova escreveu:
> > > > refcount_t type and corresponding API should be
> > > > used instead of atomic_t when the variable is used as
> > > > a reference counter. This allows to avoid accidental
> > > > refcounter overflows that might lead to use-after-free
> > > > situations.
> > > >  #define __CGROUP_H__
> > > >
> > > > -#include <linux/atomic.h>
> > > > +#include <linux/refcount.h>
> > >
> > > So this is the first one, I was expecting the copy from
> > > include/linux/refcount.h to be made to tools/include/linux/refcount.h,
> > > as was done for tools/include/linux/atomic.h and all the other stuff in
> > > tools/include/
> > >
> > > See:
> > >
> > > commit c4b6014e8bb0c8d47fe5c71ebc604f31091e5d3f
> > > Author: Arnaldo Carvalho de Melo <acme@...hat.com>
> > > Date:   Mon Jul 11 10:28:48 2016 -0300
> > >
> > >     tools: Add copy of perf_event.h to tools/include/linux/
> > >
> > > --------------
> > >
> > > For one of the reasons we've been doing this.
> 
> > Hm.. I have taken a look on it and I am confused.  refcount.h is not
> > exactly standalone header and seems to bring in quite some many
> > dependencies to other headers (linux/bug.h, linux/mutex.h etc.), which
> > are not present in tools headers dirs.
> 
> > I tried to compile perf tool as a start, copied the refcount.h to
> > tools/include/linux/ and somewhere after it wanted me to bring the
> > 10th header I stopped, because this cannot be right, or?
> 
> So, it doesn't have to be a straight copy, and it just shows the problem
> with using the kernel headers directly, i.e. tools/perf/ uses atomic.h,
> and uses that for refcounting, but not all of include/linux/refcount.h
> should be copied to tools/include/linux/refcount.h.

Oh, this is a good hint. Actually when I drop the *_lock and *_mutex_lock functions
(which are not needed by tools anyway), indeed most of the issues with header inclusions are gone. 
However, there are still some additional atomic functions needed that are not present in current atomic headers of tools.

> 
> I'll try doing the work, that way I'll read about this new stuff, will
> come back here with what I find, so you can continue on the kernel bits
> for now, ok?

Sure, if you want to take it over, nobosy won't complain! We need many of such changes merged and not everyone is so nice to help :)
I think after the needed headers/functions from refcount/atomic are in place in tools, the current patches should compile with no or almost no changes, so hopefully it still makes your work easier!

Best Regards,
Elena.
> 
> - Arnaldo