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

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Date:   Wed, 10 Mar 2021 09:44:08 +0800
From:   Tonghao Zhang <xiangxia.m.yue@...il.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: sock: simplify tw proto registration

On Wed, Mar 10, 2021 at 1:39 AM Alexander Duyck
<alexander.duyck@...il.com> wrote:
>
> 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.
Hi, thanks for your review.
if twsk_prot_init failed, (kasprintf, or slab alloc), we will invoke
the tw_prot_cleanup() to clean up
the sources allocated.
1. kfree(twsk_prot->twsk_slab_name); // if name is NULL, kfree() will
return directly
2. kmem_cache_destroy(twsk_prot->twsk_slab); // if slab is NULL,
kmem_cache_destroy() will return directly too.
so we don't care what err in twsk_prot_init().

and req_prot_cleanup() will clean up all sources allocated for req_prot_init().

> >  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
> >



-- 
Best regards, Tonghao