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mptcp: introduce mptcp-level backlog 

We are soon using it for incoming data processing.
MPTCP can't leverage the sk_backlog, as the latter is processed
before the release callback, and such callback for MPTCP releases
and re-acquire the socket spinlock, breaking the sk_backlog processing
assumption.

Add a skb backlog list inside the mptcp sock struct, and implement
basic helper to transfer packet to and purge such list.

Packets in the backlog are memory accounted and still use the incoming
subflow receive memory, to allow back-pressure. The backlog size is
implicitly bounded to the sum of subflows rcvbuf.

When a subflow is closed, references from the backlog to such sock
are removed.

No packet is currently added to the backlog, so no functional changes
intended here.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20251121-net-next-mptcp-memcg-backlog-imp-v1-13-1f34b6c1e0b1@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2025-11-21 18:02:12 +01:00 committed by Jakub Kicinski
parent 9db5b3cec4
commit ee458a3f31
3 changed files with 97 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
net/mptcp/mptcp_diag.c
View File

@ -195,7 +195,8 @@ static void mptcp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
struct mptcp_sock *msk = mptcp_sk(sk);
struct mptcp_info *info = _info;
r->idiag_rqueue = sk_rmem_alloc_get(sk);
r->idiag_rqueue = sk_rmem_alloc_get(sk) +
READ_ONCE(mptcp_sk(sk)->backlog_len);
r->idiag_wqueue = sk_wmem_alloc_get(sk);
if (inet_sk_state_load(sk) == TCP_LISTEN) {

76
net/mptcp/protocol.c
View File

@ -659,6 +659,39 @@ static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk)
}
}
static void __mptcp_add_backlog(struct sock *sk,
struct mptcp_subflow_context *subflow,
struct sk_buff *skb)
{
struct mptcp_sock *msk = mptcp_sk(sk);
struct sk_buff *tail = NULL;
bool fragstolen;
int delta;
if (unlikely(sk->sk_state == TCP_CLOSE)) {
kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_CLOSE);
return;
}
/* Try to coalesce with the last skb in our backlog */
if (!list_empty(&msk->backlog_list))
tail = list_last_entry(&msk->backlog_list, struct sk_buff, list);
if (tail && MPTCP_SKB_CB(skb)->map_seq == MPTCP_SKB_CB(tail)->end_seq &&
skb->sk == tail->sk &&
__mptcp_try_coalesce(sk, tail, skb, &fragstolen, &delta)) {
skb->truesize -= delta;
kfree_skb_partial(skb, fragstolen);
__mptcp_subflow_lend_fwdmem(subflow, delta);
WRITE_ONCE(msk->backlog_len, msk->backlog_len + delta);
return;
}
list_add_tail(&skb->list, &msk->backlog_list);
mptcp_subflow_lend_fwdmem(subflow, skb);
WRITE_ONCE(msk->backlog_len, msk->backlog_len + skb->truesize);
}
static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
struct sock *ssk)
{
@ -705,8 +738,13 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
size_t len = skb->len - offset;
mptcp_init_skb(ssk, skb, offset, len);
if (true) {
mptcp_subflow_lend_fwdmem(subflow, skb);
ret = __mptcp_move_skb(sk, skb) || ret;
ret |= __mptcp_move_skb(sk, skb);
} else {
__mptcp_add_backlog(sk, subflow, skb);
}
seq += len;
if (unlikely(map_remaining < len)) {
@ -2531,6 +2569,9 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
struct mptcp_subflow_context *subflow)
{
struct mptcp_sock *msk = mptcp_sk(sk);
struct sk_buff *skb;
/* The first subflow can already be closed and still in the list */
if (subflow->close_event_done)
return;
@ -2540,6 +2581,17 @@ void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
if (sk->sk_state == TCP_ESTABLISHED)
mptcp_event(MPTCP_EVENT_SUB_CLOSED, mptcp_sk(sk), ssk, GFP_KERNEL);
/* Remove any reference from the backlog to this ssk; backlog skbs consume
* space in the msk receive queue, no need to touch sk->sk_rmem_alloc
*/
list_for_each_entry(skb, &msk->backlog_list, list) {
if (skb->sk != ssk)
continue;
atomic_sub(skb->truesize, &skb->sk->sk_rmem_alloc);
skb->sk = NULL;
}
/* subflow aborted before reaching the fully_established status
* attempt the creation of the next subflow
*/
@ -2769,12 +2821,31 @@ static void mptcp_mp_fail_no_response(struct mptcp_sock *msk)
unlock_sock_fast(ssk, slow);
}
static void mptcp_backlog_purge(struct sock *sk)
{
struct mptcp_sock *msk = mptcp_sk(sk);
struct sk_buff *tmp, *skb;
LIST_HEAD(backlog);
mptcp_data_lock(sk);
list_splice_init(&msk->backlog_list, &backlog);
msk->backlog_len = 0;
mptcp_data_unlock(sk);
list_for_each_entry_safe(skb, tmp, &backlog, list) {
mptcp_borrow_fwdmem(sk, skb);
kfree_skb_reason(skb, SKB_DROP_REASON_SOCKET_CLOSE);
}
sk_mem_reclaim(sk);
}
static void mptcp_do_fastclose(struct sock *sk)
{
struct mptcp_subflow_context *subflow, *tmp;
struct mptcp_sock *msk = mptcp_sk(sk);
mptcp_set_state(sk, TCP_CLOSE);
mptcp_backlog_purge(sk);
/* Explicitly send the fastclose reset as need */
if (__mptcp_check_fallback(msk))
@ -2853,11 +2924,13 @@ static void __mptcp_init_sock(struct sock *sk)
INIT_LIST_HEAD(&msk->conn_list);
INIT_LIST_HEAD(&msk->join_list);
INIT_LIST_HEAD(&msk->rtx_queue);
INIT_LIST_HEAD(&msk->backlog_list);
INIT_WORK(&msk->work, mptcp_worker);
msk->out_of_order_queue = RB_ROOT;
msk->first_pending = NULL;
msk->timer_ival = TCP_RTO_MIN;
msk->scaling_ratio = TCP_DEFAULT_SCALING_RATIO;
msk->backlog_len = 0;
WRITE_ONCE(msk->first, NULL);
inet_csk(sk)->icsk_sync_mss = mptcp_sync_mss;
@ -3234,6 +3307,7 @@ static void mptcp_destroy_common(struct mptcp_sock *msk)
struct sock *sk = (struct sock *)msk;
__mptcp_clear_xmit(sk);
mptcp_backlog_purge(sk);
/* join list will be eventually flushed (with rst) at sock lock release time */
mptcp_for_each_subflow_safe(msk, subflow, tmp)

25
net/mptcp/protocol.h
View File

@ -357,6 +357,9 @@ struct mptcp_sock {
* allow_infinite_fallback and
* allow_join
*/
struct list_head backlog_list; /* protected by the data lock */
u32 backlog_len;
};
#define mptcp_data_lock(sk) spin_lock_bh(&(sk)->sk_lock.slock)
@ -407,6 +410,7 @@ static inline int mptcp_space_from_win(const struct sock *sk, int win)
static inline int __mptcp_space(const struct sock *sk)
{
return mptcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) -
READ_ONCE(mptcp_sk(sk)->backlog_len) -
sk_rmem_alloc_get(sk));
}
@ -655,23 +659,32 @@ static inline void mptcp_borrow_fwdmem(struct sock *sk, struct sk_buff *skb)
{
struct sock *ssk = skb->sk;
/* The subflow just lend the skb fwd memory, and we know that the skb
* is only accounted on the incoming subflow rcvbuf.
/* The subflow just lend the skb fwd memory; if the subflow meanwhile
* closed, mptcp_close_ssk() already released the ssk rcv memory.
*/
DEBUG_NET_WARN_ON_ONCE(skb->destructor);
skb->sk = NULL;
sk_forward_alloc_add(sk, skb->truesize);
if (!ssk)
return;
atomic_sub(skb->truesize, &ssk->sk_rmem_alloc);
skb->sk = NULL;
}
static inline void
__mptcp_subflow_lend_fwdmem(struct mptcp_subflow_context *subflow, int size)
{
int frag = (subflow->lent_mem_frag + size) & (PAGE_SIZE - 1);
subflow->lent_mem_frag = frag;
}
static inline void
mptcp_subflow_lend_fwdmem(struct mptcp_subflow_context *subflow,
struct sk_buff *skb)
{
int frag = (subflow->lent_mem_frag + skb->truesize) & (PAGE_SIZE - 1);
__mptcp_subflow_lend_fwdmem(subflow, skb->truesize);
skb->destructor = NULL;
subflow->lent_mem_frag = frag;
}
static inline u64