linux-kernel - Re: [PATCH v2 2/2] nfp: flower: Remove usage of the deprecated ida_simple

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Date:   Thu, 9 Jun 2022 09:32:52 +0200
From:   Simon Horman <simon.horman@...igine.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        oss-drivers@...igine.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2 2/2] nfp: flower: Remove usage of the deprecated
 ida_simple_xxx API

On Thu, Jun 09, 2022 at 07:11:14AM +0200, Christophe JAILLET wrote:
> Le 10/02/2022 à 23:35, Christophe JAILLET a écrit :
> > Use ida_alloc_xxx()/ida_free() instead to
> > ida_simple_get()/ida_simple_remove().
> > The latter is deprecated and more verbose.
> > 
> > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > ---
> >   .../net/ethernet/netronome/nfp/flower/tunnel_conf.c    | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/netronome/nfp/flower/tunnel_conf.c b/drivers/net/ethernet/netronome/nfp/flower/tunnel_conf.c
> > index 9244b35e3855..c71bd555f482 100644
> > --- a/drivers/net/ethernet/netronome/nfp/flower/tunnel_conf.c
> > +++ b/drivers/net/ethernet/netronome/nfp/flower/tunnel_conf.c
> > @@ -942,8 +942,8 @@ nfp_tunnel_add_shared_mac(struct nfp_app *app, struct net_device *netdev,
> >   	if (!nfp_mac_idx) {
> >   		/* Assign a global index if non-repr or MAC is now shared. */
> >   		if (entry || !port) {
> > -			ida_idx = ida_simple_get(&priv->tun.mac_off_ids, 0,
> > -						 NFP_MAX_MAC_INDEX, GFP_KERNEL);
> > +			ida_idx = ida_alloc_max(&priv->tun.mac_off_ids,
> > +						NFP_MAX_MAC_INDEX, GFP_KERNEL);
> >   			if (ida_idx < 0)
> >   				return ida_idx;
> > @@ -998,7 +998,7 @@ nfp_tunnel_add_shared_mac(struct nfp_app *app, struct net_device *netdev,
> >   	kfree(entry);
> >   err_free_ida:
> >   	if (ida_idx != -1)
> > -		ida_simple_remove(&priv->tun.mac_off_ids, ida_idx);
> > +		ida_free(&priv->tun.mac_off_ids, ida_idx);
> >   	return err;
> >   }
> > @@ -1061,7 +1061,7 @@ nfp_tunnel_del_shared_mac(struct nfp_app *app, struct net_device *netdev,
> >   		}
> >   		ida_idx = nfp_tunnel_get_ida_from_global_mac_idx(entry->index);
> > -		ida_simple_remove(&priv->tun.mac_off_ids, ida_idx);
> > +		ida_free(&priv->tun.mac_off_ids, ida_idx);
> >   		entry->index = nfp_mac_idx;
> >   		return 0;
> >   	}
> > @@ -1081,7 +1081,7 @@ nfp_tunnel_del_shared_mac(struct nfp_app *app, struct net_device *netdev,
> >   	/* If MAC has global ID then extract and free the ida entry. */
> >   	if (nfp_tunnel_is_mac_idx_global(nfp_mac_idx)) {
> >   		ida_idx = nfp_tunnel_get_ida_from_global_mac_idx(entry->index);
> > -		ida_simple_remove(&priv->tun.mac_off_ids, ida_idx);
> > +		ida_free(&priv->tun.mac_off_ids, ida_idx);
> >   	}
> >   	kfree(entry);
> 
> Hi,
> 
> This has been merged in -next in commit 432509013f66 but for some reason I
> looked at it again.
> 
> 
> I just wanted to point out that this patch DOES change the behavior of the
> driver because ida_simple_get() is exclusive of the upper bound, while
> ida_alloc_max() is inclusive.
> 
> So, knowing that NFP_MAX_MAC_INDEX = 0xff = 255, with the previous code
> 'ida_idx' was 0 ... 254.
> Now it is 0 ... 255.
> 
> This still looks good to me, because NFP_MAX_MAC_INDEX is still not a power
> of 2.
> 
> 
> But if 255 is a reserved value for whatever reason, then this patch has
> introduced a bug (apologies for it).
> 
> The change of behavior should have been mentioned in the commit description.
> So I wanted to make sure you was aware in case a follow-up fix is needed.

Hi Christophe,

thanks for bringing this to my attention.

When I made my initial review of the patch I did not notice this subtle
change. However, subsequently, the Corigine team did notice and our
conclusion is that it is fine: the code correctly handles all expected
values including 255.

Kind regards,
Simon