linux-kernel - RE: [PATCH 14/15] futex: convert futex_pi_state.refcount to refcount

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Date:   Fri, 20 Oct 2017 14:30:13 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
cc:     'Peter Zijlstra' <peterz@...radead.org>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'linux-fsdevel@...r.kernel.org'" <linux-fsdevel@...r.kernel.org>,
        "'gregkh@...uxfoundation.org'" <gregkh@...uxfoundation.org>,
        "'viro@...iv.linux.org.uk'" <viro@...iv.linux.org.uk>,
        "'tj@...nel.org'" <tj@...nel.org>,
        "'mingo@...hat.com'" <mingo@...hat.com>,
        "'hannes@...xchg.org'" <hannes@...xchg.org>,
        "'lizefan@...wei.com'" <lizefan@...wei.com>,
        "'acme@...nel.org'" <acme@...nel.org>,
        "'alexander.shishkin@...ux.intel.com'" 
        <alexander.shishkin@...ux.intel.com>,
        "'eparis@...hat.com'" <eparis@...hat.com>,
        "'akpm@...ux-foundation.org'" <akpm@...ux-foundation.org>,
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        "'dvhart@...radead.org'" <dvhart@...radead.org>,
        "'ebiederm@...ssion.com'" <ebiederm@...ssion.com>
Subject: RE: [PATCH 14/15] futex: convert futex_pi_state.refcount to
 refcount_t

On Fri, 20 Oct 2017, Reshetova, Elena wrote:

> Since I am not really sure what to do with this futex patch, I will drop it
> from the new series that I am about to send now. 
> 
> Please let me know what exactly should I do with this patch, as I wrote 
> previously I really don't understand. 

As Peter said:

> > > Now Thomas would like you to mention the fact that refcount_t doesn't
> > > provide the exact same ordering as the atomic_t usages it replaces and
> > > I think it would be good if you could hand-wave an argument on why the
> > > futex code doesn't care.

So if you cannot come with a halfways reasonable argument then at least
make it entirely clear that refcount_t is not the same as atomic_t in terms
of ordering guarantees and you think that it does not matter but
explicitely ask for help from the developers and maintainers to look at it.

Thanks,

	tglx