linux-kernel - KVM: s390/mm: Clarification for two return value checks in gmap

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Message-ID: <7f0b7ac0-d061-9484-bc5e-bdd9e32aa42b@web.de>
Date:   Sat, 2 May 2020 17:43:01 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        Christian Bornträger <borntraeger@...ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Cornelia Huck <cohuck@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: KVM: s390/mm: Clarification for two return value checks in
 gmap_shadow()

Hello,

I have tried another small script out for the semantic patch language.
This source code analysis approach points out that the function “gmap_find_shadow”
is called two times by the function “gmap_shadow”.
https://elixir.bootlin.com/linux/v5.7-rc3/source/arch/s390/mm/gmap.c#L1628
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/arch/s390/mm/gmap.c

Null pointer checks are performed at these places.
The function “gmap_find_shadow” is documented in the same source file
that the pointer “ERR_PTR(-EAGAIN)” can eventually be returned.
Are the referenced gmap data structures always initialised here?

Regards,
Markus