linux-kernel - Re: [PATCH v2] net/mlx5e: Use refcount

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Message-ID: <CANhBUQ2H5MU0m2xM0AkJGPf7+MJBZ3Eq5rR0kgeOoKRi4q1j6Q@mail.gmail.com>
Date:   Sun, 4 Aug 2019 22:44:47 +0800
From:   Chuhong Yuan <hslester96@...il.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "David S . Miller" <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, linux-rdma@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net/mlx5e: Use refcount_t for refcount

On Sun, Aug 4, 2019 at 8:59 PM Leon Romanovsky <leon@...nel.org> wrote:
>
> On Sat, Aug 03, 2019 at 12:48:28AM +0800, Chuhong Yuan wrote:
> > refcount_t is better for reference counters since its
> > implementation can prevent overflows.
> > So convert atomic_t ref counters to refcount_t.
>
> I'm not thrilled to see those automatic conversion patches, especially
> for flows which can't overflow. There is nothing wrong in using atomic_t
> type of variable, do you have in mind flow which will cause to overflow?
>
> Thanks

I have to say that these patches are not done automatically...
Only the detection of problems is done by a script.
All conversions are done manually.

I am not sure whether the flow can cause an overflow.
But I think it is hard to ensure that a data path is impossible
to have problems in any cases including being attacked.

So I think it is better to do this minor revision to prevent
potential risk, just like we have done in mlx5/core/cq.c.

Regards,
Chuhong

> >
> > Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> > ---
> > Changes in v2:
> >   - Add #include.
> >
> >  drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c | 9 +++++----
> >  1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c b/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> > index b9d4f4e19ff9..148b55c3db7a 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/lib/vxlan.c
> > @@ -32,6 +32,7 @@
> >
> >  #include <linux/kernel.h>
> >  #include <linux/module.h>
> > +#include <linux/refcount.h>
> >  #include <linux/mlx5/driver.h>
> >  #include <net/vxlan.h>
> >  #include "mlx5_core.h"
> > @@ -48,7 +49,7 @@ struct mlx5_vxlan {
> >
> >  struct mlx5_vxlan_port {
> >       struct hlist_node hlist;
> > -     atomic_t refcount;
> > +     refcount_t refcount;
> >       u16 udp_port;
> >  };
> >
> > @@ -113,7 +114,7 @@ int mlx5_vxlan_add_port(struct mlx5_vxlan *vxlan, u16 port)
> >
> >       vxlanp = mlx5_vxlan_lookup_port(vxlan, port);
> >       if (vxlanp) {
> > -             atomic_inc(&vxlanp->refcount);
> > +             refcount_inc(&vxlanp->refcount);
> >               return 0;
> >       }
> >
> > @@ -137,7 +138,7 @@ int mlx5_vxlan_add_port(struct mlx5_vxlan *vxlan, u16 port)
> >       }
> >
> >       vxlanp->udp_port = port;
> > -     atomic_set(&vxlanp->refcount, 1);
> > +     refcount_set(&vxlanp->refcount, 1);
> >
> >       spin_lock_bh(&vxlan->lock);
> >       hash_add(vxlan->htable, &vxlanp->hlist, port);
> > @@ -170,7 +171,7 @@ int mlx5_vxlan_del_port(struct mlx5_vxlan *vxlan, u16 port)
> >               goto out_unlock;
> >       }
> >
> > -     if (atomic_dec_and_test(&vxlanp->refcount)) {
> > +     if (refcount_dec_and_test(&vxlanp->refcount)) {
> >               hash_del(&vxlanp->hlist);
> >               remove = true;
> >       }
> > --
> > 2.20.1
> >