From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DE0F282ED for ; Fri, 6 Sep 2024 17:27:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725643631; cv=none; b=sTcVC/Qi1Y6QtBhkdRonj5yx0iD/SqbO0C8LPGx+em9Rb+jx64AEsK38gU3eRBFGL9SyIZr0Am+0CXFv1B3YmQV9FTuiGRwYOlxBoJ3LqP1bkrqhJzkqLa4F2Cu3BZL3j8JNgqUgD9fsVLzFzqlc9Q32LesTMBp+d1jZ/Xcghzg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725643631; c=relaxed/simple; bh=Xl9GhYfH33n8+vrvQQByZM+HhAj2WaK6ParsMKtSHbA=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=S2mI7//6R9QuTjKabBYxt5ewvSL/QXfMCdT/Hf1vZ0Li2AsD8+7NZgGyeWmlLB8vkT/QvPAHfnJjRJyy5n0fSx+Wql/fvcD829IJ5e/EXxcicuZyfTw+dnRYmTr2yCbd0TuZoaY9C0H71RIE/EkXs58fwRS22Hb3bneN/4Hztjs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=ul12t6dN; arc=none smtp.client-ip=91.218.175.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="ul12t6dN" Message-ID: <1f17d828-5d0f-4050-be4b-8840feb8de76@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1725643625; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bVHMVg2i3Sgc9zlacM0Rr3Aexo5lbdLJRO1gCLW9714=; b=ul12t6dNieyKCi76aywADX/VGQkh7S/Omcu2TyEqrsts89gnyoQghOqLpYWUIMjnDYmmTV SU0hUs+pvC1vgp0usAyP4ZTAJ0AoTtbt2E8EzY9DTejaABVu9c7+eeHR7aItgYD+Vq2A1/ mGYA2LvQqS16QmUUFhX1PHvkfSjpox0= Date: Fri, 6 Sep 2024 18:27:00 +0100 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH net-next v3 2/4] net_tstamp: add SCM_TS_OPT_ID for TCP sockets To: Willem de Bruijn , Willem de Bruijn Cc: netdev@vger.kernel.org, David Ahern , Jason Xing , Jakub Kicinski , Simon Horman , Paolo Abeni 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> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Vadim Fedorenko In-Reply-To: <66db1f004a0c_29a3852944d@willemb.c.googlers.com.notmuch> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 06/09/2024 16:25, 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. > > The most obvious solution would be to set the flag in sk_tsflags > itself. But then the cmsg would no long work on a per request basis: > either the socket uses OPT_ID with counter or OPT_ID_CMSG. > > Good that we catch this now before the ABI is finalized. > > If necessary TCP semantics can diverge from datagrams. So we could > punt on this. But it's not ideal. I have done proof of concept code which uses hwtsamp as a storage for custom tskey in case of TCP: diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a52638363ea5..40ed49e61bf7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -5414,8 +5414,6 @@ static void __skb_complete_tx_timestamp(struct sk_buff *skb, serr->header.h4.iif = skb->dev ? skb->dev->ifindex : 0; if (READ_ONCE(sk->sk_tsflags) & SOF_TIMESTAMPING_OPT_ID) { serr->ee.ee_data = skb_shinfo(skb)->tskey; - if (sk_is_tcp(sk)) - serr->ee.ee_data -= atomic_read(&sk->sk_tskey); } err = sock_queue_err_skb(sk, skb); @@ -5450,6 +5448,8 @@ void skb_complete_tx_timestamp(struct sk_buff *skb, * but only if the socket refcount is not zero. */ if (likely(refcount_inc_not_zero(&sk->sk_refcnt))) { + if (sk_is_tcp(sk) && (READ_ONCE(sk->sk_tsflags) & SOF_TIMESTAMPING_OPT_ID) && skb_hwtstamps(skb)->hwtstamp) + skb_shinfo(skb)->tskey = (u32)skb_hwtstamps(skb)->hwtstamp; *skb_hwtstamps(skb) = *hwtstamps; __skb_complete_tx_timestamp(skb, sk, SCM_TSTAMP_SND, false); sock_put(sk); @@ -5509,6 +5509,12 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, skb_shinfo(skb)->tskey = skb_shinfo(orig_skb)->tskey; } + if (sk_is_tcp(sk) && (tsflags & SOF_TIMESTAMPING_OPT_ID)) { + if (skb_hwtstamps(orig_skb)->hwtstamp) + skb_shinfo(skb)->tskey = (u32)skb_hwtstamps(orig_skb)->hwtstamp; + else + skb_shinfo(skb)->tskey -= atomic_read(&sk->sk_tskey); + } if (hwtstamps) *skb_hwtstamps(skb) = *hwtstamps; else diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 0d3decc13a99..1a161a2155b5 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -488,9 +488,8 @@ static void tcp_tx_timestamp(struct sock *sk, struct sockcm_cookie *sockc) tcb->txstamp_ack = 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; + skb_hwtstamps(skb)->hwtstamp = sockc->ts_opt_id; + shinfo->tskey = TCP_SKB_CB(skb)->seq + skb->len - 1; } } } Looks like we can add u32 tskey field in skb_shared_hwtstamps and reuse it. netdev_data field is only used on RX timestamp side, so should be fine to reuse. WDYT?