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From: Abhishek Chauhan <quic_abchauha@quicinc.com>
To: "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Andrew Halaney <ahalaney@redhat.com>,
        Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
        Martin KaFai Lau <martin.lau@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Daniel Borkmann <daniel@iogearbox.net>
Cc: kernel@quicinc.com
Subject: [PATCH net-next v2] Revert "net: Re-use and set mono_delivery_time bit for userspace tstamp packets"
Date: Wed, 13 Mar 2024 18:08:13 -0700
Message-Id: <20240314010813.1418521-1-quic_abchauha@quicinc.com>
Precedence: bulk
MIME-Version: 1.0
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This reverts commit 30bb896b98fce7d823a96fc02cd69be30384a5cc.
The patch currently broke the bpf selftest test_tc_dtime because
uapi field __sk_buff->tstamp_type depends on skb->mono_delivery_time which
does not necessarily mean mono with the original fix as the bit was re-used
for userspace timestamp as well to avoid tstamp reset in the forwarding 
path. To solve this we need to keep mono_delivery_time as ease and 
introduce another bit called user_delivery_time and fall back to the 
initial proposal of setting the user_delivery_time bit based on 
sk_clockid set from userspace.

Link: https://lore.kernel.org/netdev/bc037db4-58bb-4861-ac31-a361a93841d3@linux.dev/
Signed-off-by: Abhishek Chauhan <quic_abchauha@quicinc.com>
---
Changes since v1
- Took care of Jakub's comment to explain more about the 
  revert commit 
- Added Link to the discussion of the problem found in the 
  original commit. 

 include/linux/skbuff.h | 6 +++---
 net/ipv4/ip_output.c   | 1 -
 net/ipv4/raw.c         | 1 -
 net/ipv6/ip6_output.c  | 2 +-
 net/ipv6/raw.c         | 2 +-
 net/packet/af_packet.c | 4 +---
 6 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4726298d4ed4..2dde34c29203 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -817,9 +817,9 @@ typedef unsigned char *sk_buff_data_t;
  *	@decrypted: Decrypted SKB
  *	@slow_gro: state present at GRO time, slower prepare step required
  *	@mono_delivery_time: When set, skb->tstamp has the
- *		delivery_time in mono clock base (i.e., EDT) or a clock base chosen
- *		by SO_TXTIME. If zero, skb->tstamp has the (rcv) timestamp at
- *		ingress.
+ *		delivery_time in mono clock base (i.e. EDT).  Otherwise, the
+ *		skb->tstamp has the (rcv) timestamp at ingress and
+ *		delivery_time at egress.
  *	@napi_id: id of the NAPI struct this skb came from
  *	@sender_cpu: (aka @napi_id) source CPU in XPS
  *	@alloc_cpu: CPU which did the skb allocation.
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index ff1df64c5697..5b5a0adb927f 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1455,7 +1455,6 @@ struct sk_buff *__ip_make_skb(struct sock *sk,
 	skb->priority = (cork->tos != -1) ? cork->priority: READ_ONCE(sk->sk_priority);
 	skb->mark = cork->mark;
 	skb->tstamp = cork->transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
 	/*
 	 * Steal rt from cork.dst to avoid a pair of atomic_inc/atomic_dec
 	 * on dst refcount
diff --git a/net/ipv4/raw.c b/net/ipv4/raw.c
index c4c29fc5b73f..aea89326c697 100644
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -353,7 +353,6 @@ static int raw_send_hdrinc(struct sock *sk, struct flowi4 *fl4,
 	skb->priority = READ_ONCE(sk->sk_priority);
 	skb->mark = sockc->mark;
 	skb->tstamp = sockc->transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
 	skb_dst_set(skb, &rt->dst);
 	*rtp = NULL;
 
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 2fc1d03dc07d..a722a43dd668 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -1922,7 +1922,7 @@ struct sk_buff *__ip6_make_skb(struct sock *sk,
 	skb->priority = READ_ONCE(sk->sk_priority);
 	skb->mark = cork->base.mark;
 	skb->tstamp = cork->base.transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
+
 	ip6_cork_steal_dst(skb, cork);
 	IP6_INC_STATS(net, rt->rt6i_idev, IPSTATS_MIB_OUTREQUESTS);
 	if (proto == IPPROTO_ICMPV6) {
diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index 13f54f8eea35..03dbb874c363 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -616,7 +616,7 @@ static int rawv6_send_hdrinc(struct sock *sk, struct msghdr *msg, int length,
 	skb->priority = READ_ONCE(sk->sk_priority);
 	skb->mark = sockc->mark;
 	skb->tstamp = sockc->transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
+
 	skb_put(skb, length);
 	skb_reset_network_header(skb);
 	iph = ipv6_hdr(skb);
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 0db31ca4982d..c9bbc2686690 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2057,7 +2057,7 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg,
 	skb->priority = READ_ONCE(sk->sk_priority);
 	skb->mark = READ_ONCE(sk->sk_mark);
 	skb->tstamp = sockc.transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
+
 	skb_setup_tx_timestamp(skb, sockc.tsflags);
 
 	if (unlikely(extra_len == 4))
@@ -2586,7 +2586,6 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
 	skb->priority = READ_ONCE(po->sk.sk_priority);
 	skb->mark = READ_ONCE(po->sk.sk_mark);
 	skb->tstamp = sockc->transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
 	skb_setup_tx_timestamp(skb, sockc->tsflags);
 	skb_zcopy_set_nouarg(skb, ph.raw);
 
@@ -3065,7 +3064,6 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	skb->priority = READ_ONCE(sk->sk_priority);
 	skb->mark = sockc.mark;
 	skb->tstamp = sockc.transmit_time;
-	skb->mono_delivery_time = !!skb->tstamp;
 
 	if (unlikely(extra_len == 4))
 		skb->no_fcs = 1;
-- 
2.25.1