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From:   Michael Chan <michael.chan@broadcom.com>
Date:   Wed, 31 Jul 2019 10:48:28 -0700
Message-ID: <CACKFLin6kXeHrCR_U8R+CYDWCW2c=N5m_0SNupO7rqZmaL3SGQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] bnxt_en: Use refcount_t for refcount
To:     Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc:     Chuhong Yuan <hslester96@gmail.com>,
        "David S . Miller" <davem@davemloft.net>,
        Network Development <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Wed, Jul 31, 2019 at 9:06 AM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> On Wed, Jul 31, 2019 at 8:22 AM Chuhong Yuan <hslester96@gmail.com> wrote:
> >
> > refcount_t is better for reference counters since its
> > implementation can prevent overflows.
> > So convert atomic_t ref counters to refcount_t.
> >
> > Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
> > ---
> >  drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c | 8 ++++----
> >  drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.h | 2 +-
> >  2 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> > index fc77caf0a076..eb7ed34639e2 100644
> > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ulp.c
> > @@ -49,7 +49,7 @@ static int bnxt_register_dev(struct bnxt_en_dev *edev, int ulp_id,
> >                         return -ENOMEM;
> >         }
> >
> > -       atomic_set(&ulp->ref_count, 0);
> > +       refcount_set(&ulp->ref_count, 0);
>
> One feature of refcount_t is that it warns on refcount_inc from 0 to
> detect possible use-after_free. It appears that that can trigger here?
>

I think that's right.  We need to change the driver to start counting
from 1 instead of 0 if we convert to refcount.