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From: "Reshetova, Elena" <elena.reshetova@intel.com>
To: David Howells <dhowells@redhat.com>
CC: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-afs@lists.infradead.org" <linux-afs@lists.infradead.org>,
        "peterz@infradead.org" <peterz@infradead.org>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        Hans Liljestrand <ishkamiel@gmail.com>,
        "Kees Cook" <keescook@chromium.org>,
        David Windsor <dwindsor@gmail.com>
Subject: RE: [PATCH 1/4] fs, afs: convert afs_cell.usage from atomic_t to
 refcount_t
Thread-Topic: [PATCH 1/4] fs, afs: convert afs_cell.usage from atomic_t to
 refcount_t
Thread-Index: AQHSjFlH0Aza8UMUrUiQNZ8uKmd18aF1NTYAgAAPUBA=
Date: Wed, 22 Feb 2017 17:19:49 +0000
Message-ID: <2236FBA76BA1254E88B949DDB74E612B41C4EF59@IRSMSX102.ger.corp.intel.com>
References: <1487691808-11289-2-git-send-email-elena.reshetova@intel.com>
 <1487691808-11289-1-git-send-email-elena.reshetova@intel.com>
 <12908.1487780160@warthog.procyon.org.uk>
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> Elena Reshetova <elena.reshetova@intel.com> wrote:
> 
> > 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.
> 
> This causes an assertion failure because cells aren't immediately destroyed
> when their refcount reaches 0, but may be resurrected provided the cache lock
> is held.  However, attempting to increment the 0 refcount does nothing, not
> even giving a warning.

This is strange, it is supposed to give a warning I think now when it is even not inlined. 
Peter, am I confusing smth?

> 
> So please place a hold on this patch.  I will check the other AFS patches also.
> 

Thank you very much David for testing the patches! 
I guess for this one and other two patches it means that if we want to do the atomic_t --> refcount_t conversions, 
we need to do +1 on the whole counting scheme to avoid issues around reaching zero.  
Do you see this approach reasonable? I can give it a try, if it makes sense in your opinion. 

Best Regards,
Elena.