Re: [PATCH RFC net 1/2] tcp: Add TIME_WAIT sockets in bhash2.

[Joanne Koong <joannelkoong@gmail.com>]

On Thu, Dec 22, 2022 at 7:06 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Thu, 2022-12-22 at 00:12 +0900, Kuniyuki Iwashima wrote:
> > Jiri Slaby reported regression of bind() with a simple repro. [0]
> >
> > The repro creates a TIME_WAIT socket and tries to bind() a new socket
> > with the same local address and port.  Before commit 28044fc1d495 ("net:
> > Add a bhash2 table hashed by port and address"), the bind() failed with
> > -EADDRINUSE, but now it succeeds.
> >
> > The cited commit should have put TIME_WAIT sockets into bhash2; otherwise,
> > inet_bhash2_conflict() misses TIME_WAIT sockets when validating bind()
> > requests if the address is not a wildcard one.

(resending my reply because it wasn't in plaintext mode)

Thanks for adding this! I hadn't realized TIME_WAIT sockets also are
considered when checking against inet bind conflicts.

>
> How does keeping the timewait sockets inside bhash2 affect the bind
> loopup performance? I fear that could defeat completely the goal of
> 28044fc1d495, on quite busy server we could have quite a bit of tw with
> the same address/port. If so, we could even consider reverting
> 28044fc1d495.
>

Can you clarify what you mean by bind loopup?

> > [0]: https://lore.kernel.org/netdev/6b971a4e-c7d8-411e-1f92-fda29b5b2fb9@kernel.org/
> >
> > Fixes: 28044fc1d495 ("net: Add a bhash2 table hashed by port and address")
> > Reported-by: Jiri Slaby <jirislaby@kernel.org>
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > ---
> >  include/net/inet_timewait_sock.h |  2 ++
> >  include/net/sock.h               |  5 +++--
> >  net/ipv4/inet_hashtables.c       |  5 +++--
> >  net/ipv4/inet_timewait_sock.c    | 31 +++++++++++++++++++++++++++++--
> >  4 files changed, 37 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/net/inet_timewait_sock.h b/include/net/inet_timewait_sock.h
> > index 5b47545f22d3..c46ed239ad9a 100644
> > --- a/include/net/inet_timewait_sock.h
> > +++ b/include/net/inet_timewait_sock.h
> > @@ -44,6 +44,7 @@ struct inet_timewait_sock {
> >  #define tw_bound_dev_if              __tw_common.skc_bound_dev_if
> >  #define tw_node                      __tw_common.skc_nulls_node
> >  #define tw_bind_node         __tw_common.skc_bind_node
> > +#define tw_bind2_node                __tw_common.skc_bind2_node
> >  #define tw_refcnt            __tw_common.skc_refcnt
> >  #define tw_hash                      __tw_common.skc_hash
> >  #define tw_prot                      __tw_common.skc_prot
> > @@ -73,6 +74,7 @@ struct inet_timewait_sock {
> >       u32                     tw_priority;
> >       struct timer_list       tw_timer;
> >       struct inet_bind_bucket *tw_tb;
> > +     struct inet_bind2_bucket        *tw_tb2;
> >  };
> >  #define tw_tclass tw_tos
> >
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index dcd72e6285b2..aaec985c1b5b 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -156,6 +156,7 @@ typedef __u64 __bitwise __addrpair;
> >   *   @skc_tw_rcv_nxt: (aka tw_rcv_nxt) TCP window next expected seq number
> >   *           [union with @skc_incoming_cpu]
> >   *   @skc_refcnt: reference count
> > + *   @skc_bind2_node: bind node in the bhash2 table
> >   *
> >   *   This is the minimal network layer representation of sockets, the header
> >   *   for struct sock and struct inet_timewait_sock.
> > @@ -241,6 +242,7 @@ struct sock_common {
> >               u32             skc_window_clamp;
> >               u32             skc_tw_snd_nxt; /* struct tcp_timewait_sock */
> >       };
> > +     struct hlist_node       skc_bind2_node;
>
> I *think* it would be better adding a tw_bind2_node field to the
> inet_timewait_sock struct, so that we leave unmodified the request
> socket and we don't change the struct sock binary layout. That could
> affect performances moving hot fields on different cachelines.
>
+1. The rest of this patch LGTM.

>
> Thanks,
>
> Paolo
>