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mptcp: avoid a few atomic ops in the rx path
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Extending the data_lock scope in mptcp_incoming_option
we can use that to protect both snd_una and wnd_end.
In the typical case, we will have a single atomic op instead of 2

Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Paolo Abeni authored and Jakub Kicinski committed Dec 1, 2020
1 parent 724cfd2 commit 7439d68
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Showing 4 changed files with 34 additions and 43 deletions.
2 changes: 1 addition & 1 deletion net/mptcp/mptcp_diag.c
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Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,7 @@ static void mptcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
info->mptcpi_flags = flags;
info->mptcpi_token = READ_ONCE(msk->token);
info->mptcpi_write_seq = READ_ONCE(msk->write_seq);
info->mptcpi_snd_una = atomic64_read(&msk->snd_una);
info->mptcpi_snd_una = READ_ONCE(msk->snd_una);
info->mptcpi_rcv_nxt = READ_ONCE(msk->ack_seq);
unlock_sock_fast(sk, slow);
}
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33 changes: 13 additions & 20 deletions net/mptcp/options.c
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Original file line number Diff line number Diff line change
Expand Up @@ -833,15 +833,17 @@ static void ack_update_msk(struct mptcp_sock *msk,
const struct sock *ssk,
struct mptcp_options_received *mp_opt)
{
u64 new_snd_una, snd_una, old_snd_una = atomic64_read(&msk->snd_una);
u64 new_wnd_end, wnd_end, old_wnd_end = atomic64_read(&msk->wnd_end);
u64 snd_nxt = READ_ONCE(msk->snd_nxt);
u64 new_wnd_end, new_snd_una, snd_nxt = READ_ONCE(msk->snd_nxt);
struct sock *sk = (struct sock *)msk;
u64 old_snd_una;

mptcp_data_lock(sk);

/* avoid ack expansion on update conflict, to reduce the risk of
* wrongly expanding to a future ack sequence number, which is way
* more dangerous than missing an ack
*/
old_snd_una = msk->snd_una;
new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);

/* ACK for data not even sent yet? Ignore. */
Expand All @@ -850,26 +852,17 @@ static void ack_update_msk(struct mptcp_sock *msk,

new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;

while (after64(new_wnd_end, old_wnd_end)) {
wnd_end = old_wnd_end;
old_wnd_end = atomic64_cmpxchg(&msk->wnd_end, wnd_end,
new_wnd_end);
if (old_wnd_end == wnd_end) {
if (mptcp_send_head(sk))
mptcp_schedule_work(sk);
break;
}
if (after64(new_wnd_end, msk->wnd_end)) {
msk->wnd_end = new_wnd_end;
if (mptcp_send_head(sk))
mptcp_schedule_work(sk);
}

while (after64(new_snd_una, old_snd_una)) {
snd_una = old_snd_una;
old_snd_una = atomic64_cmpxchg(&msk->snd_una, snd_una,
new_snd_una);
if (old_snd_una == snd_una) {
mptcp_data_acked(sk);
break;
}
if (after64(new_snd_una, old_snd_una)) {
msk->snd_una = new_snd_una;
__mptcp_data_acked(sk);
}
mptcp_data_unlock(sk);
}

bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
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34 changes: 16 additions & 18 deletions net/mptcp/protocol.c
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ static struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk)
/* Returns end sequence number of the receiver's advertised window */
static u64 mptcp_wnd_end(const struct mptcp_sock *msk)
{
return atomic64_read(&msk->wnd_end);
return READ_ONCE(msk->wnd_end);
}

static bool mptcp_is_tcpsk(struct sock *sk)
Expand Down Expand Up @@ -358,7 +358,7 @@ static void mptcp_check_data_fin_ack(struct sock *sk)
/* Look for an acknowledged DATA_FIN */
if (((1 << sk->sk_state) &
(TCPF_FIN_WAIT1 | TCPF_CLOSING | TCPF_LAST_ACK)) &&
msk->write_seq == atomic64_read(&msk->snd_una)) {
msk->write_seq == READ_ONCE(msk->snd_una)) {
mptcp_stop_timer(sk);

WRITE_ONCE(msk->snd_data_fin_enable, 0);
Expand Down Expand Up @@ -764,7 +764,7 @@ bool mptcp_schedule_work(struct sock *sk)
return false;
}

void mptcp_data_acked(struct sock *sk)
void __mptcp_data_acked(struct sock *sk)
{
mptcp_reset_timer(sk);

Expand Down Expand Up @@ -997,11 +997,11 @@ static void mptcp_clean_una(struct sock *sk)
* plain TCP
*/
if (__mptcp_check_fallback(msk))
atomic64_set(&msk->snd_una, msk->snd_nxt);
msk->snd_una = READ_ONCE(msk->snd_nxt);

mptcp_data_lock(sk);
snd_una = atomic64_read(&msk->snd_una);

mptcp_data_lock(sk);
snd_una = msk->snd_una;
list_for_each_entry_safe(dfrag, dtmp, &msk->rtx_queue, list) {
if (after64(dfrag->data_seq + dfrag->data_len, snd_una))
break;
Expand Down Expand Up @@ -1282,10 +1282,12 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
/* Zero window and all data acked? Probe. */
avail_size = mptcp_check_allowed_size(msk, data_seq, avail_size);
if (avail_size == 0) {
if (skb || atomic64_read(&msk->snd_una) != msk->snd_nxt)
u64 snd_una = READ_ONCE(msk->snd_una);

if (skb || snd_una != msk->snd_nxt)
return 0;
zero_window_probe = true;
data_seq = atomic64_read(&msk->snd_una) - 1;
data_seq = snd_una - 1;
avail_size = 1;
}

Expand Down Expand Up @@ -1994,12 +1996,8 @@ static void mptcp_retransmit_handler(struct sock *sk)
{
struct mptcp_sock *msk = mptcp_sk(sk);

if (atomic64_read(&msk->snd_una) == READ_ONCE(msk->snd_nxt)) {
mptcp_stop_timer(sk);
} else {
set_bit(MPTCP_WORK_RTX, &msk->flags);
mptcp_schedule_work(sk);
}
set_bit(MPTCP_WORK_RTX, &msk->flags);
mptcp_schedule_work(sk);
}

static void mptcp_retransmit_timer(struct timer_list *t)
Expand Down Expand Up @@ -2621,8 +2619,8 @@ struct sock *mptcp_sk_clone(const struct sock *sk,

msk->write_seq = subflow_req->idsn + 1;
msk->snd_nxt = msk->write_seq;
atomic64_set(&msk->snd_una, msk->write_seq);
atomic64_set(&msk->wnd_end, msk->snd_nxt + req->rsk_rcv_wnd);
msk->snd_una = msk->write_seq;
msk->wnd_end = msk->snd_nxt + req->rsk_rcv_wnd;

if (mp_opt->mp_capable) {
msk->can_ack = true;
Expand Down Expand Up @@ -2658,7 +2656,7 @@ void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk)
if (msk->rcvq_space.space == 0)
msk->rcvq_space.space = TCP_INIT_CWND * TCP_MSS_DEFAULT;

atomic64_set(&msk->wnd_end, msk->snd_nxt + tcp_sk(ssk)->snd_wnd);
WRITE_ONCE(msk->wnd_end, msk->snd_nxt + tcp_sk(ssk)->snd_wnd);
}

static struct sock *mptcp_accept(struct sock *sk, int flags, int *err,
Expand Down Expand Up @@ -2918,7 +2916,7 @@ void mptcp_finish_connect(struct sock *ssk)
WRITE_ONCE(msk->ack_seq, ack_seq);
WRITE_ONCE(msk->rcv_wnd_sent, ack_seq);
WRITE_ONCE(msk->can_ack, 1);
atomic64_set(&msk->snd_una, msk->write_seq);
WRITE_ONCE(msk->snd_una, msk->write_seq);

mptcp_pm_new_connection(msk, 0);

Expand Down
8 changes: 4 additions & 4 deletions net/mptcp/protocol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -222,8 +222,8 @@ struct mptcp_sock {
struct sock *last_snd;
int snd_burst;
int old_wspace;
atomic64_t snd_una;
atomic64_t wnd_end;
u64 snd_una;
u64 wnd_end;
unsigned long timer_ival;
u32 token;
int rmem_pending;
Expand Down Expand Up @@ -321,7 +321,7 @@ static inline struct mptcp_data_frag *mptcp_rtx_tail(const struct sock *sk)
{
struct mptcp_sock *msk = mptcp_sk(sk);

if (!before64(msk->snd_nxt, atomic64_read(&msk->snd_una)))
if (!before64(msk->snd_nxt, READ_ONCE(msk->snd_una)))
return NULL;

return list_last_entry(&msk->rtx_queue, struct mptcp_data_frag, list);
Expand Down Expand Up @@ -495,7 +495,7 @@ void mptcp_rcv_space_init(struct mptcp_sock *msk, const struct sock *ssk);
void mptcp_data_ready(struct sock *sk, struct sock *ssk);
bool mptcp_finish_join(struct sock *sk);
bool mptcp_schedule_work(struct sock *sk);
void mptcp_data_acked(struct sock *sk);
void __mptcp_data_acked(struct sock *sk);
void mptcp_subflow_eof(struct sock *sk);
bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit);
void __mptcp_flush_join_list(struct mptcp_sock *msk);
Expand Down

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