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net: implement lockless SO_MAX_PACING_RATE
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SO_MAX_PACING_RATE setsockopt() does not need to hold
the socket lock, because sk->sk_pacing_rate readers
can run fine if the value is changed by other threads,
after adding READ_ONCE() accessors.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Oct 1, 2023
1 parent 2a4319c commit 28b24f9
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Showing 6 changed files with 37 additions and 33 deletions.
2 changes: 1 addition & 1 deletion include/trace/events/mptcp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -44,7 +44,7 @@ TRACE_EVENT(mptcp_subflow_get_send,
ssk = mptcp_subflow_tcp_sock(subflow);
if (ssk && sk_fullsock(ssk)) {
__entry->snd_wnd = tcp_sk(ssk)->snd_wnd;
__entry->pace = ssk->sk_pacing_rate;
__entry->pace = READ_ONCE(ssk->sk_pacing_rate);
} else {
__entry->snd_wnd = 0;
__entry->pace = 0;
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40 changes: 21 additions & 19 deletions net/core/sock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1160,6 +1160,27 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
WRITE_ONCE(sk->sk_busy_poll_budget, val);
return 0;
#endif
case SO_MAX_PACING_RATE:
{
unsigned long ulval = (val == ~0U) ? ~0UL : (unsigned int)val;
unsigned long pacing_rate;

if (sizeof(ulval) != sizeof(val) &&
optlen >= sizeof(ulval) &&
copy_from_sockptr(&ulval, optval, sizeof(ulval))) {
return -EFAULT;
}
if (ulval != ~0UL)
cmpxchg(&sk->sk_pacing_status,
SK_PACING_NONE,
SK_PACING_NEEDED);
/* Pairs with READ_ONCE() from sk_getsockopt() */
WRITE_ONCE(sk->sk_max_pacing_rate, ulval);
pacing_rate = READ_ONCE(sk->sk_pacing_rate);
if (ulval < pacing_rate)
WRITE_ONCE(sk->sk_pacing_rate, ulval);
return 0;
}
}

sockopt_lock_sock(sk);
Expand Down Expand Up @@ -1423,25 +1444,6 @@ int sk_setsockopt(struct sock *sk, int level, int optname,
break;


case SO_MAX_PACING_RATE:
{
unsigned long ulval = (val == ~0U) ? ~0UL : (unsigned int)val;

if (sizeof(ulval) != sizeof(val) &&
optlen >= sizeof(ulval) &&
copy_from_sockptr(&ulval, optval, sizeof(ulval))) {
ret = -EFAULT;
break;
}
if (ulval != ~0UL)
cmpxchg(&sk->sk_pacing_status,
SK_PACING_NONE,
SK_PACING_NEEDED);
/* Pairs with READ_ONCE() from sk_getsockopt() */
WRITE_ONCE(sk->sk_max_pacing_rate, ulval);
sk->sk_pacing_rate = min(sk->sk_pacing_rate, ulval);
break;
}
case SO_INCOMING_CPU:
reuseport_update_incoming_cpu(sk, val);
break;
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13 changes: 7 additions & 6 deletions net/ipv4/tcp_bbr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -258,7 +258,7 @@ static unsigned long bbr_bw_to_pacing_rate(struct sock *sk, u32 bw, int gain)
u64 rate = bw;

rate = bbr_rate_bytes_per_sec(sk, rate, gain);
rate = min_t(u64, rate, sk->sk_max_pacing_rate);
rate = min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate));
return rate;
}

Expand All @@ -278,7 +278,8 @@ static void bbr_init_pacing_rate_from_rtt(struct sock *sk)
}
bw = (u64)tcp_snd_cwnd(tp) * BW_UNIT;
do_div(bw, rtt_us);
sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain);
WRITE_ONCE(sk->sk_pacing_rate,
bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain));
}

/* Pace using current bw estimate and a gain factor. */
Expand All @@ -290,14 +291,14 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)

if (unlikely(!bbr->has_seen_rtt && tp->srtt_us))
bbr_init_pacing_rate_from_rtt(sk);
if (bbr_full_bw_reached(sk) || rate > sk->sk_pacing_rate)
sk->sk_pacing_rate = rate;
if (bbr_full_bw_reached(sk) || rate > READ_ONCE(sk->sk_pacing_rate))
WRITE_ONCE(sk->sk_pacing_rate, rate);
}

/* override sysctl_tcp_min_tso_segs */
__bpf_kfunc static u32 bbr_min_tso_segs(struct sock *sk)
{
return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
return READ_ONCE(sk->sk_pacing_rate) < (bbr_min_tso_rate >> 3) ? 1 : 2;
}

static u32 bbr_tso_segs_goal(struct sock *sk)
Expand All @@ -309,7 +310,7 @@ static u32 bbr_tso_segs_goal(struct sock *sk)
* driver provided sk_gso_max_size.
*/
bytes = min_t(unsigned long,
sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift),
READ_ONCE(sk->sk_pacing_rate) >> READ_ONCE(sk->sk_pacing_shift),
GSO_LEGACY_MAX_SIZE - 1 - MAX_TCP_HEADER);
segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));

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4 changes: 2 additions & 2 deletions net/ipv4/tcp_input.c
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Original file line number Diff line number Diff line change
Expand Up @@ -927,8 +927,8 @@ static void tcp_update_pacing_rate(struct sock *sk)
* without any lock. We want to make sure compiler wont store
* intermediate values in this location.
*/
WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
sk->sk_max_pacing_rate));
WRITE_ONCE(sk->sk_pacing_rate,
min_t(u64, rate, READ_ONCE(sk->sk_max_pacing_rate)));
}

/* Calculate rto without backoff. This is the second half of Van Jacobson's
Expand Down
9 changes: 5 additions & 4 deletions net/ipv4/tcp_output.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1201,7 +1201,7 @@ static void tcp_update_skb_after_send(struct sock *sk, struct sk_buff *skb,
struct tcp_sock *tp = tcp_sk(sk);

if (sk->sk_pacing_status != SK_PACING_NONE) {
unsigned long rate = sk->sk_pacing_rate;
unsigned long rate = READ_ONCE(sk->sk_pacing_rate);

/* Original sch_fq does not pace first 10 MSS
* Note that tp->data_segs_out overflows after 2^32 packets,
Expand Down Expand Up @@ -1973,7 +1973,7 @@ static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
unsigned long bytes;
u32 r;

bytes = sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift);
bytes = READ_ONCE(sk->sk_pacing_rate) >> READ_ONCE(sk->sk_pacing_shift);

r = tcp_min_rtt(tcp_sk(sk)) >> READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_rtt_log);
if (r < BITS_PER_TYPE(sk->sk_gso_max_size))
Expand Down Expand Up @@ -2553,15 +2553,16 @@ static bool tcp_small_queue_check(struct sock *sk, const struct sk_buff *skb,

limit = max_t(unsigned long,
2 * skb->truesize,
sk->sk_pacing_rate >> READ_ONCE(sk->sk_pacing_shift));
READ_ONCE(sk->sk_pacing_rate) >> READ_ONCE(sk->sk_pacing_shift));
if (sk->sk_pacing_status == SK_PACING_NONE)
limit = min_t(unsigned long, limit,
READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_limit_output_bytes));
limit <<= factor;

if (static_branch_unlikely(&tcp_tx_delay_enabled) &&
tcp_sk(sk)->tcp_tx_delay) {
u64 extra_bytes = (u64)sk->sk_pacing_rate * tcp_sk(sk)->tcp_tx_delay;
u64 extra_bytes = (u64)READ_ONCE(sk->sk_pacing_rate) *
tcp_sk(sk)->tcp_tx_delay;

/* TSQ is based on skb truesize sum (sk_wmem_alloc), so we
* approximate our needs assuming an ~100% skb->truesize overhead.
Expand Down
2 changes: 1 addition & 1 deletion net/sched/sch_fq.c
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Original file line number Diff line number Diff line change
Expand Up @@ -668,7 +668,7 @@ static struct sk_buff *fq_dequeue(struct Qdisc *sch)
*/
if (!skb->tstamp) {
if (skb->sk)
rate = min(skb->sk->sk_pacing_rate, rate);
rate = min(READ_ONCE(skb->sk->sk_pacing_rate), rate);

if (rate <= q->low_rate_threshold) {
f->credit = 0;
Expand Down

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