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

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Message-ID: <20170222153754.GA20447@kernel.org>
Date:   Wed, 22 Feb 2017 12:37:54 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
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.

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?

- Arnaldo