linux-kernel - Re: [PATCH 3/3] xen/blkback: Use refcount

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Message-ID: <CANhBUQ3rN+nLOHFGEAaQV6rB7Ob2wf9iLUiP8pjWM0NDMC4Qxg@mail.gmail.com>
Date:   Tue, 13 Aug 2019 14:10:24 +0800
From:   Chuhong Yuan <hslester96@...il.com>
To:     Roger Pau Monné <roger.pau@...rix.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, xen-devel@...ts.xenproject.org,
        linux-block@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] xen/blkback: Use refcount_t for refcount

On Thu, Aug 8, 2019 at 9:35 PM Roger Pau Monné <roger.pau@...rix.com> wrote:
>
> On Thu, Aug 08, 2019 at 09:11:00PM +0800, Chuhong Yuan wrote:
> > Reference counters are preferred to use refcount_t instead of
> > atomic_t.
> > This is because the implementation of refcount_t can prevent
> > overflows and detect possible use-after-free.
> > So convert atomic_t ref counters to refcount_t.
>
> Thanks!
>
> I think there are more reference counters in blkback than
> the one you fixed. There's also an inflight field in xen_blkif_ring,
> and a pendcnt in pending_req which look like possible candidates to
> switch to use refcount_t, have you looked into switching those two
> also?
>

It seems that xen_blkif_ring::inflight is 0-based and cannot be directly
converted to refcount_t.
This is because the implementation of refcount_t will warn on increasing
a 0 ref count.
Therefore I only convert pending_req::pendcnt in v2.

> Roger.