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Message-ID: <CANn89iLZx-SiV0BqHkEt9vS4LZzDxW2omvfOvNX6XWSRPFs7sw@mail.gmail.com> Date: Wed, 29 Nov 2023 19:34:07 +0100 From: Eric Dumazet <edumazet@...gle.com> To: Dmitry Safonov <dima@...sta.com> Cc: David Ahern <dsahern@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>, linux-kernel@...r.kernel.org, Dmitry Safonov <0x7f454c46@...il.com>, Francesco Ruggeri <fruggeri05@...il.com>, Salam Noureddine <noureddine@...sta.com>, Simon Horman <horms@...nel.org>, netdev@...r.kernel.org Subject: Re: [PATCH v4 6/7] net/tcp: Store SNEs + SEQs on ao_info On Wed, Nov 29, 2023 at 7:14 PM Dmitry Safonov <dima@...sta.com> wrote: > > On 11/29/23 18:09, Eric Dumazet wrote: > > On Wed, Nov 29, 2023 at 5:57 PM Dmitry Safonov <dima@...sta.com> 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. > >> > > > > This will not work on 32bit kernels ? > > Yeah, unsure if there's someone who wants to run BGP on 32bit box, so at > this moment it's already limited: > > config TCP_AO > bool "TCP: Authentication Option (RFC5925)" > select CRYPTO > select TCP_SIGPOOL > depends on 64BIT && IPV6 != m # seq-number extension needs WRITE_ONCE(u64) > Oh well, this seems quite strange to have such a limitation. > Probably, if there will be a person who is interested in this, it can > get a spinlock for !CONFIG_64BIT. > > > Unless ao->snd_sne and ao->rcv_sneare only read/written under the > > socket lock (and in this case no READ_ONCE()/WRITE_ONCE() should be > > necessary) > You have not commented on where these are read without the socket lock held ? tcp_ao_get_repair() can lock the socket. In TW state, I guess these values can not be changed ? I think you can remove all these READ_ONCE()/WRITE_ONCE() which are not needed, or please add a comment if they really are. Then, you might be able to remove the 64BIT dependency ...
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