linux-kernel - Re: [PATCH 2/5] vfio/spapr_tce: use pinned_vm instead of locked

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Message-ID: <01000168e29daf0a-cb3a9394-e3dd-4d88-ad3c-31df1f9ec052-000000@email.amazonses.com>
Date:   Tue, 12 Feb 2019 16:50:11 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>
cc:     Daniel Jordan <daniel.m.jordan@...cle.com>, jgg@...pe.ca,
        akpm@...ux-foundation.org, dave@...olabs.net, jack@...e.cz,
        linux-mm@...ck.org, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org, alex.williamson@...hat.com,
        paulus@...abs.org, benh@...nel.crashing.org, mpe@...erman.id.au,
        hao.wu@...el.com, atull@...nel.org, mdf@...nel.org
Subject: Re: [PATCH 2/5] vfio/spapr_tce: use pinned_vm instead of locked_vm
 to account pinned pages

On Tue, 12 Feb 2019, Alexey Kardashevskiy wrote:

> Now it is 3 independent accesses (actually 4 but the last one is
> diagnostic) with no locking around them. Why do not we need a lock
> anymore precisely? Thanks,

Updating a regular counter is racy and requires a lock. It was converted
to be an atomic which can be incremented without a race.