netdev - Re: [PATCH] net: sock: simplify tw proto registration

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Date:   Tue, 9 Mar 2021 09:39:40 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Tonghao Zhang <xiangxia.m.yue@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sock: simplify tw proto registration

On Mon, Mar 8, 2021 at 7:15 PM <xiangxia.m.yue@...il.com> wrote:
>
> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
>
> Introduce a new function twsk_prot_init, inspired by
> req_prot_init, to simplify the "proto_register" function.
>
> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
> ---
>  net/core/sock.c | 44 ++++++++++++++++++++++++++++----------------
>  1 file changed, 28 insertions(+), 16 deletions(-)
>
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 0ed98f20448a..610de4295101 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -3475,6 +3475,32 @@ static int req_prot_init(const struct proto *prot)
>         return 0;
>  }
>
> +static int twsk_prot_init(const struct proto *prot)
> +{
> +       struct timewait_sock_ops *twsk_prot = prot->twsk_prot;
> +
> +       if (!twsk_prot)
> +               return 0;
> +
> +       twsk_prot->twsk_slab_name = kasprintf(GFP_KERNEL, "tw_sock_%s",
> +                                             prot->name);
> +       if (!twsk_prot->twsk_slab_name)
> +               return -ENOMEM;
> +
> +       twsk_prot->twsk_slab =
> +               kmem_cache_create(twsk_prot->twsk_slab_name,
> +                                 twsk_prot->twsk_obj_size, 0,
> +                                 SLAB_ACCOUNT | prot->slab_flags,
> +                                 NULL);
> +       if (!twsk_prot->twsk_slab) {
> +               pr_crit("%s: Can't create timewait sock SLAB cache!\n",
> +                       prot->name);
> +               return -ENOMEM;
> +       }
> +
> +       return 0;
> +}
> +

So one issue here is that you have two returns but they both have the
same error clean-up outside of the function. It might make more sense
to look at freeing the kasprintf if the slab allocation fails and then
using the out_free_request_sock_slab jump label below if the slab
allocation failed.

>  int proto_register(struct proto *prot, int alloc_slab)
>  {
>         int ret = -ENOBUFS;
> @@ -3496,22 +3522,8 @@ int proto_register(struct proto *prot, int alloc_slab)
>                 if (req_prot_init(prot))
>                         goto out_free_request_sock_slab;
>
> -               if (prot->twsk_prot != NULL) {
> -                       prot->twsk_prot->twsk_slab_name = kasprintf(GFP_KERNEL, "tw_sock_%s", prot->name);
> -
> -                       if (prot->twsk_prot->twsk_slab_name == NULL)
> -                               goto out_free_request_sock_slab;
> -
> -                       prot->twsk_prot->twsk_slab =
> -                               kmem_cache_create(prot->twsk_prot->twsk_slab_name,
> -                                                 prot->twsk_prot->twsk_obj_size,
> -                                                 0,
> -                                                 SLAB_ACCOUNT |
> -                                                 prot->slab_flags,
> -                                                 NULL);
> -                       if (prot->twsk_prot->twsk_slab == NULL)
> -                               goto out_free_timewait_sock_slab;
> -               }
> +               if (twsk_prot_init(prot))
> +                       goto out_free_timewait_sock_slab;

So assuming the code above takes care of freeing the slab name in case
of slab allocation failure then this would be better off jumping to
out_free_request_sock_slab.

>         }
>
>         mutex_lock(&proto_list_mutex);
> --
> 2.27.0
>