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

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Date:   Tue, 9 Mar 2021 18:42:24 -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 Tue, Mar 9, 2021 at 5:48 PM Tonghao Zhang <xiangxia.m.yue@...il.com> wrote:
>
> 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().

I see. Okay so the expectation is that tw_prot_cleanup will take care
of a partially initialized timewait_sock_ops.

With that being the case the one change I would ask you to make would
be to look at moving the function up so it is just below
tw_prot_cleanup so it is obvious that the two are meant to be paired
rather than placing it after req_prot_init.

Otherwise the patch set itself looks good to me.

Reviewed-by: Alexander Duyck <alexanderduyck@...com>