Messages in this thread Patch in this message | | | Date | Thu, 7 Dec 2023 10:52:36 +0000 | From | Simon Horman <> | Subject | Re: [PATCH v4 6/7] net/tcp: Store SNEs + SEQs on ao_info |
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On Mon, Dec 04, 2023 at 05:08:20PM +0000, Dmitry Safonov wrote: > Hi Simon, > > On 12/2/23 17:16, Simon Horman wrote: > > On Wed, Nov 29, 2023 at 04:57:20PM +0000, Dmitry Safonov wrote: > >> RFC 5925 (6.2): > >>> TCP-AO emulates a 64-bit sequence number space by inferring when to > >>> increment the high-order 32-bit portion (the SNE) based on > >>> transitions in the low-order portion (the TCP sequence number). > >> > >> snd_sne and rcv_sne are the upper 4 bytes of extended SEQ number. > >> Unfortunately, reading two 4-bytes pointers can't be performed > >> atomically (without synchronization). > >> > >> In order to avoid locks on TCP fastpath, let's just double-account for > >> SEQ changes: snd_una/rcv_nxt will be lower 4 bytes of snd_sne/rcv_sne. > >> > >> Fixes: 64382c71a557 ("net/tcp: Add TCP-AO SNE support") > >> Signed-off-by: Dmitry Safonov <dima@arista.com> > > > > ... > > > >> diff --git a/include/net/tcp_ao.h b/include/net/tcp_ao.h > >> index 647781080613..b8ef25d4b632 100644 > >> --- a/include/net/tcp_ao.h > >> +++ b/include/net/tcp_ao.h > >> @@ -121,8 +121,8 @@ struct tcp_ao_info { > >> * - for time-wait sockets the basis is tw_rcv_nxt/tw_snd_nxt. > >> * tw_snd_nxt is not expected to change, while tw_rcv_nxt may. > >> */ > >> - u32 snd_sne; > >> - u32 rcv_sne; > >> + u64 snd_sne; > >> + u64 rcv_sne; > >> refcount_t refcnt; /* Protects twsk destruction */ > >> struct rcu_head rcu; > >> }; > > > > Hi Dmitry, > > > > In tcp_ao.c:tcp_ao_connect_init() there is a local > > variable: > > > > struct tcp_ao_info *ao_info; > > > > And the following assignment occurs: > > > > ao_info->snd_sne = htonl(tp->write_seq); > > > > Is this still correct in light of the change of the type of snd_sne? > > Thanks for the report. > Yes, it's correct as lower 4-bytes are initialized as initial SEQ. > I'll add a cast for it if I'll go with v5 for this patch.
Thanks Dmitry,
I think that would address my concern.
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