netdev - Re: [Patch net 1/2] l2tp: convert l2tp_tunnel

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Date:   Sat, 7 Jan 2023 11:48:15 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Saeed Mahameed <saeed@...nel.org>
Cc:     netdev@...r.kernel.org, g.nault@...halink.fr,
        Cong Wang <cong.wang@...edance.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [Patch net 1/2] l2tp: convert l2tp_tunnel_list to idr

On Sat, Jan 07, 2023 at 10:25:04AM -0800, Saeed Mahameed wrote:
> On 05 Jan 11:13, Cong Wang wrote:
> > From: Cong Wang <cong.wang@...edance.com>
> > 
> > l2tp uses l2tp_tunnel_list to track all registered tunnels and
> > to allocate tunnel ID's. IDR can do the same job.
> > 
> > More importantly, with IDR we can hold the ID before a successful
> > registration so that we don't need to worry about late error
> > hanlding, it is not easy to rollback socket changes.
> > 
> > This is a preparation for the following fix.
> > 
> > Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> > Cc: Guillaume Nault <g.nault@...halink.fr>
> > Cc: Jakub Sitnicki <jakub@...udflare.com>
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Signed-off-by: Cong Wang <cong.wang@...edance.com>
> > ---
> > net/l2tp/l2tp_core.c    | 93 ++++++++++++++++++++++-------------------
> > net/l2tp/l2tp_core.h    |  3 +-
> > net/l2tp/l2tp_netlink.c |  3 +-
> > net/l2tp/l2tp_ppp.c     |  3 +-
> > 4 files changed, 57 insertions(+), 45 deletions(-)
> > 
> > diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
> > index 9a1415fe3fa7..570249a91c6c 100644
> > --- a/net/l2tp/l2tp_core.c
> > +++ b/net/l2tp/l2tp_core.c
> > @@ -104,9 +104,9 @@ static struct workqueue_struct *l2tp_wq;
> > /* per-net private data for this module */
> > static unsigned int l2tp_net_id;
> > struct l2tp_net {
> > -	struct list_head l2tp_tunnel_list;
> > -	/* Lock for write access to l2tp_tunnel_list */
> > -	spinlock_t l2tp_tunnel_list_lock;
> > +	/* Lock for write access to l2tp_tunnel_idr */
> > +	spinlock_t l2tp_tunnel_idr_lock;
> > +	struct idr l2tp_tunnel_idr;
> > 	struct hlist_head l2tp_session_hlist[L2TP_HASH_SIZE_2];
> > 	/* Lock for write access to l2tp_session_hlist */
> > 	spinlock_t l2tp_session_hlist_lock;
> > @@ -208,13 +208,10 @@ struct l2tp_tunnel *l2tp_tunnel_get(const struct net *net, u32 tunnel_id)
> > 	struct l2tp_tunnel *tunnel;
> > 
> > 	rcu_read_lock_bh();
> > -	list_for_each_entry_rcu(tunnel, &pn->l2tp_tunnel_list, list) {
> > -		if (tunnel->tunnel_id == tunnel_id &&
> > -		    refcount_inc_not_zero(&tunnel->ref_count)) {
> > -			rcu_read_unlock_bh();
> > -
> > -			return tunnel;
> > -		}
> > +	tunnel = idr_find(&pn->l2tp_tunnel_idr, tunnel_id);
> > +	if (tunnel && refcount_inc_not_zero(&tunnel->ref_count)) {
> > +		rcu_read_unlock_bh();
> > +		return tunnel;
> > 	}
> > 	rcu_read_unlock_bh();
> > 
> > @@ -224,13 +221,14 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_get);
> > 
> > struct l2tp_tunnel *l2tp_tunnel_get_nth(const struct net *net, int nth)
> > {
> > -	const struct l2tp_net *pn = l2tp_pernet(net);
> > +	struct l2tp_net *pn = l2tp_pernet(net);
> 
> Any reason to remove the const keyword ?

Yes, GCC complained about discarding const in idr_for_each_entry_ul().

Thanks.