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[34.150.132.193]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7a9a7967e7asm3609485a.38.2024.09.06.16.50.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Sep 2024 16:50:31 -0700 (PDT) Date: Fri, 06 Sep 2024 19:50:30 -0400 From: Willem de Bruijn To: Vadim Fedorenko , Willem de Bruijn , Willem de Bruijn Cc: netdev@vger.kernel.org, David Ahern , Jason Xing , Jakub Kicinski , Simon Horman , Paolo Abeni Message-ID: <66db9546f0ecb_2a33ef294bc@willemb.c.googlers.com.notmuch> In-Reply-To: References: <20240904113153.2196238-1-vadfed@meta.com> <20240904113153.2196238-3-vadfed@meta.com> <3e4add99-6b57-4fe1-9ee1-519c80cf7cf5@linux.dev> <66d9debb2d2ea_1eae1a2943d@willemb.c.googlers.com.notmuch> <66db1f004a0c_29a3852944d@willemb.c.googlers.com.notmuch> <66db2eef2d90_29c8c329475@willemb.c.googlers.com.notmuch> Subject: Re: [PATCH net-next v3 2/4] net_tstamp: add SCM_TS_OPT_ID for TCP sockets Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Vadim Fedorenko wrote: > On 06/09/2024 17:33, Willem de Bruijn wrote: > > Willem de Bruijn wrote: > >> Vadim Fedorenko wrote: > >>> On 05/09/2024 17:39, Willem de Bruijn wrote: > >>>> Vadim Fedorenko wrote: > >>>>> On 04/09/2024 12:31, Vadim Fedorenko wrote: > >>>>>> TCP sockets have different flow for providing timestamp OPT_ID value. > >>>>>> Adjust the code to support SCM_TS_OPT_ID option for TCP sockets. > >>>>>> > >>>>>> Signed-off-by: Vadim Fedorenko > >>>>>> --- > >>>>>> net/ipv4/tcp.c | 13 +++++++++---- > >>>>>> 1 file changed, 9 insertions(+), 4 deletions(-) > >>>>>> > >>>>>> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > >>>>>> index 8a5680b4e786..5553a8aeee80 100644 > >>>>>> --- a/net/ipv4/tcp.c > >>>>>> +++ b/net/ipv4/tcp.c > >>>>>> @@ -474,9 +474,10 @@ void tcp_init_sock(struct sock *sk) > >>>>>> } > >>>>>> EXPORT_SYMBOL(tcp_init_sock); > >>>>>> > >>>>>> -static void tcp_tx_timestamp(struct sock *sk, u16 tsflags) > >>>>>> +static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc) > >>>>>> { > >>>>>> struct sk_buff *skb = tcp_write_queue_tail(sk); > >>>>>> + u32 tsflags = sockc->tsflags; > >>>>>> > >>>>>> if (tsflags && skb) { > >>>>>> struct skb_shared_info *shinfo = skb_shinfo(skb); > >>>>>> @@ -485,8 +486,12 @@ static void tcp_tx_timestamp(struct sock *sk, u16 tsflags) > >>>>>> sock_tx_timestamp(sk, tsflags, &shinfo->tx_flags); > >>>>>> if (tsflags & SOF_TIMESTAMPING_TX_ACK) > >>>>>> tcb->txstamp_ack = 1; > >>>>>> - if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK) > >>>>>> - shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1; > >>>>>> + if (tsflags & SOF_TIMESTAMPING_TX_RECORD_MASK) { > >>>>>> + if (tsflags & SOCKCM_FLAG_TS_OPT_ID) > >>>>>> + shinfo->tskey = sockc->ts_opt_id; > >>>>>> + else > >>>>>> + shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1; > >>>>>> + } > >>>>>> } > >>>>>> } > >>>>>> > >>>>>> @@ -1318,7 +1323,7 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size) > >>>>>> > >>>>>> out: > >>>>>> if (copied) { > >>>>>> - tcp_tx_timestamp(sk, sockc.tsflags); > >>>>>> + tcp_tx_timestamp(sk, &sockc); > >>>>>> tcp_push(sk, flags, mss_now, tp->nonagle, size_goal); > >>>>>> } > >>>>>> out_nopush: > >>>>> > >>>>> Hi Willem, > >>>>> > >>>>> Unfortunately, these changes are not enough to enable custom OPT_ID for > >>>>> TCP sockets. There are some functions which rewrite shinfo->tskey in TCP > >>>>> flow: > >>>>> > >>>>> tcp_skb_collapse_tstamp() > >>>>> tcp_fragment_tstamp() > >>>>> tcp_gso_tstamp() > >>>>> > >>>>> I believe the last one breaks tests, but the problem is that there is no > >>>>> easy way to provide the flag of constant tskey to it. Only > >>>>> shinfo::tx_flags are available at the caller side and we have already > >>>>> discussed that we shouldn't use the last bit of this field. > >>>>> > >>>>> So, how should we deal with the problem? Or is it better to postpone > >>>>> support for TCP sockets in this case? > >>>> > >>>> Are you sure that this is a problem. These functions pass on the > >>>> skb_shinfo(skb)->ts_key from one skb to another. > >>> > >>> Yes, you are right, the problem is in a different place. > >>> > >>> __skb_complete_tx_timestamp receives skb with shinfo->tskey equal to > >>> provided by cmsg. But for TCP sockets it unconditionally adjusts ee_data > >>> value: > >>> > >>> if (sk_is_tcp(sk)) > >>> serr->ee.ee_data -= atomic_read(&sk->sk_tskey); > >>> > >>> It happens because of assumption that for TCP sockets shinfo::tskey will > >>> have sequence number and the logic has to recalculate it back to the > >>> bytes sent. The same logic exists in all TCP TX timestamping functions > >>> (mentioned in the previous mail) and may trigger some unexpected > >>> behavior. To fix the issue we have to provide some kind of signal that > >>> tskey value is provided from user-space and shouldn't be changed. And we > >>> have to have it somewhere in skb info. Again, tx_flags looks like the > >>> best candidate, but it's impossible to use. I'm thinking of using > >>> special flag in tcp_skb_cb - gonna test more, but open for other > >>> suggestions. > >> > >> Ai, that is tricky. tx_flags is full/scarce indeed. > >> > >> CB does not persist as the skb transitions between layers. > > > > Though specifically for TCP, it is possible to look up the fast > > clone on the rtx queue, whose tcp_skb_cb will be unperturbed. But > > the tcb currently does not have this data either. > > It will work fine for software timestamps, but we cannot do the same > trick in case of HW timestamps, right? I'm not really advocating it. The only user of this trick that I can find is skb_still_in_host_queue, through skb_fclone_busy. That said, it would also work for hardware, as the SKB_FCLONE_ORIG remains on the rtx queue. In the common case. But skb_fclone_busy points out edge cases, such as if a driver call skb_orphan..