linux-kernel - Re: [RFC PATCH v1 1/1] mm: zswap - Add crypto acomp/scomp framework support

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Date:   Wed, 15 Feb 2017 22:12:08 +0000
From:   Giovanni Cabiddu <giovanni.cabiddu@...el.com>
To:     Narayana Prasad Athreya <pathreya@...iumnetworks.com>
Cc:     Seth Jennings <sjenning@...hat.com>,
        Mahipal Challa <mahipalreddy2006@...il.com>,
        herbert@...dor.apana.org.au, davem@...emloft.net,
        linux-crypto@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, pathreya@...ium.com,
        vnair@...ium.com, Mahipal Challa <Mahipal.Challa@...ium.com>,
        Vishnu Nair <Vishnu.Nair@...ium.com>
Subject: Re: [RFC PATCH v1 1/1] mm: zswap - Add crypto acomp/scomp framework
 support

On Wed, Feb 15, 2017 at 07:27:30PM +0530, Narayana Prasad Athreya wrote:
> > I assume all of these crypto_acomp_[compress|decompress] calls are
> > actually synchronous,
> > not asynchronous as the name suggests.  Otherwise, this would blow up
> > quite spectacularly
> > since all the resources we use in the call get derefed/unmapped below.
> > 
> > Could an async algorithm be implement/used that would break this assumption?
> 
> The callback is set to NULL using acomp_request_set_callback(). This implies
> synchronous mode of operation. So the underlying implementation must
> complete the operation synchronously.
This assumption is not correct. An asynchronous implementation, when
it finishes processing a request, will call acomp_request_complete() which
in turn calls the callback.
If the callback is set to NULL, this function will dereference a NULL
pointer.

Regards,

-- 
Giovanni