linux-kernel - Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to refcount

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Message-Id: <20170719153546.37567fbf77861653172fa263@linux-foundation.org>
Date:   Wed, 19 Jul 2017 15:35:46 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     ebiederm@...ssion.com (Eric W. Biederman)
Cc:     Elena Reshetova <elena.reshetova@...el.com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        gregkh@...uxfoundation.org, mingo@...hat.com, adobriyan@...il.com,
        serge@...lyn.com, arozansk@...hat.com, dave@...olabs.net,
        keescook@...omium.org, Hans Liljestrand <ishkamiel@...il.com>,
        David Windsor <dwindsor@...il.com>
Subject: Re: [PATCH 1/3] ipc: convert ipc_namespace.count from atomic_t to
 refcount_t

On Sun, 09 Jul 2017 16:59:55 -0500 ebiederm@...ssion.com (Eric W. Biederman) wrote:

> Elena Reshetova <elena.reshetova@...el.com> writes:
> 
> > 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.
> 
> In this patch you can see all of the uses of the count.
> What accidental refcount overflows are possible?

I do rather dislike these conversions from the point of view of
performance overhead and general code bloat.  But I seem to have lost
that struggle and I don't think any of these are fastpath(?).