[PATCH 5.15 081/136] mptcp: stop relying on tcp_tx_skb_cache

Greg Kroah-Hartman
2022-08-29T11:11:14Z

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit f70cad1085d1e01d3ec73c1078405f906237feee ]

We want to revert the skb TX cache, but MPTCP is currently
using it unconditionally.

Rework the MPTCP tx code, so that tcp_tx_skb_cache is not
needed anymore: do the whole coalescing check, skb allocation
skb initialization/update inside mptcp_sendmsg_frag(), quite
alike the current TCP code.

Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/mptcp/protocol.c | 137 ++++++++++++++++++++++++-------------------
1 file changed, 77 insertions(+), 60 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 7f96e0c42a090..a089791414bfb 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1224,6 +1224,7 @@ static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
if (likely(__mptcp_add_ext(skb, gfp))) {
skb_reserve(skb, MAX_TCP_HEADER);
skb->reserved_tailroom = skb->end - skb->tail;
+ INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
return skb;
}
__kfree_skb(skb);
@@ -1233,31 +1234,23 @@ static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
return NULL;
}

-static bool __mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
+static struct sk_buff *__mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, gfp_t gfp)
{
struct sk_buff *skb;

- if (ssk->sk_tx_skb_cache) {
- skb = ssk->sk_tx_skb_cache;
- if (unlikely(!skb_ext_find(skb, SKB_EXT_MPTCP) &&
- !__mptcp_add_ext(skb, gfp)))
- return false;
- return true;
- }
-
skb = __mptcp_do_alloc_tx_skb(sk, gfp);
if (!skb)
- return false;
+ return NULL;

if (likely(sk_wmem_schedule(ssk, skb->truesize))) {
- ssk->sk_tx_skb_cache = skb;
- return true;
+ tcp_skb_entail(ssk, skb);
+ return skb;
}
kfree_skb(skb);
- return false;
+ return NULL;
}

-static bool mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
+static struct sk_buff *mptcp_alloc_tx_skb(struct sock *sk, struct sock *ssk, bool data_lock_held)
{
gfp_t gfp = data_lock_held ? GFP_ATOMIC : sk->sk_allocation;

@@ -1287,23 +1280,29 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
struct mptcp_sendmsg_info *info)
{
u64 data_seq = dfrag->data_seq + info->sent;
+ int offset = dfrag->offset + info->sent;
struct mptcp_sock *msk = mptcp_sk(sk);
bool zero_window_probe = false;
struct mptcp_ext *mpext = NULL;
- struct sk_buff *skb, *tail;
- bool must_collapse = false;
- int size_bias = 0;
- int avail_size;
- size_t ret = 0;
+ bool can_coalesce = false;
+ bool reuse_skb = true;
+ struct sk_buff *skb;
+ size_t copy;
+ int i;

pr_debug("msk=%p ssk=%p sending dfrag at seq=%llu len=%u already sent=%u",
msk, ssk, dfrag->data_seq, dfrag->data_len, info->sent);

+ if (WARN_ON_ONCE(info->sent > info->limit ||
+ info->limit > dfrag->data_len))
+ return 0;
+
/* compute send limit */
info->mss_now = tcp_send_mss(ssk, &info->size_goal, info->flags);
- avail_size = info->size_goal;
+ copy = info->size_goal;
+
skb = tcp_write_queue_tail(ssk);
- if (skb) {
+ if (skb && copy > skb->len) {
/* Limit the write to the size available in the
* current skb, if any, so that we create at most a new skb.
* Explicitly tells TCP internals to avoid collapsing on later
@@ -1316,62 +1315,80 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
goto alloc_skb;
}

- must_collapse = (info->size_goal > skb->len) &&
- (skb_shinfo(skb)->nr_frags < sysctl_max_skb_frags);
- if (must_collapse) {
- size_bias = skb->len;
- avail_size = info->size_goal - skb->len;
+ i = skb_shinfo(skb)->nr_frags;
+ can_coalesce = skb_can_coalesce(skb, i, dfrag->page, offset);
+ if (!can_coalesce && i >= sysctl_max_skb_frags) {
+ tcp_mark_push(tcp_sk(ssk), skb);
+ goto alloc_skb;
}
- }

+ copy -= skb->len;
+ } else {
alloc_skb:
- if (!must_collapse &&
- !mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held))
- return 0;
+ skb = mptcp_alloc_tx_skb(sk, ssk, info->data_lock_held);
+ if (!skb)
+ return -ENOMEM;
+
+ i = skb_shinfo(skb)->nr_frags;
+ reuse_skb = false;
+ mpext = skb_ext_find(skb, SKB_EXT_MPTCP);
+ }

/* Zero window and all data acked? Probe. */
- avail_size = mptcp_check_allowed_size(msk, data_seq, avail_size);
- if (avail_size == 0) {
+ copy = mptcp_check_allowed_size(msk, data_seq, copy);
+ if (copy == 0) {
u64 snd_una = READ_ONCE(msk->snd_una);

- if (skb || snd_una != msk->snd_nxt)
+ if (snd_una != msk->snd_nxt) {
+ tcp_remove_empty_skb(ssk, tcp_write_queue_tail(ssk));
return 0;
+ }
+
zero_window_probe = true;
data_seq = snd_una - 1;
- avail_size = 1;
- }
+ copy = 1;

- if (WARN_ON_ONCE(info->sent > info->limit ||
- info->limit > dfrag->data_len))
- return 0;
+ /* all mptcp-level data is acked, no skbs should be present into the
+ * ssk write queue
+ */
+ WARN_ON_ONCE(reuse_skb);
+ }

- ret = info->limit - info->sent;
- tail = tcp_build_frag(ssk, avail_size + size_bias, info->flags,
- dfrag->page, dfrag->offset + info->sent, &ret);
- if (!tail) {
- tcp_remove_empty_skb(sk, tcp_write_queue_tail(ssk));
+ copy = min_t(size_t, copy, info->limit - info->sent);
+ if (!sk_wmem_schedule(ssk, copy)) {
+ tcp_remove_empty_skb(ssk, tcp_write_queue_tail(ssk));
return -ENOMEM;
}

- /* if the tail skb is still the cached one, collapsing really happened.
- */
- if (skb == tail) {
- TCP_SKB_CB(tail)->tcp_flags &= ~TCPHDR_PSH;
- mpext->data_len += ret;
+ if (can_coalesce) {
+ skb_frag_size_add(&skb_shinfo(skb)->frags[i - 1], copy);
+ } else {
+ get_page(dfrag->page);
+ skb_fill_page_desc(skb, i, dfrag->page, offset, copy);
+ }
+
+ skb->len += copy;
+ skb->data_len += copy;
+ skb->truesize += copy;
+ sk_wmem_queued_add(ssk, copy);
+ sk_mem_charge(ssk, copy);
+ skb->ip_summed = CHECKSUM_PARTIAL;
+ WRITE_ONCE(tcp_sk(ssk)->write_seq, tcp_sk(ssk)->write_seq + copy);
+ TCP_SKB_CB(skb)->end_seq += copy;
+ tcp_skb_pcount_set(skb, 0);
+
+ /* on skb reuse we just need to update the DSS len */
+ if (reuse_skb) {
+ TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_PSH;
+ mpext->data_len += copy;
WARN_ON_ONCE(zero_window_probe);
goto out;
}

- mpext = skb_ext_find(tail, SKB_EXT_MPTCP);
- if (WARN_ON_ONCE(!mpext)) {
- /* should never reach here, stream corrupted */
- return -EINVAL;
- }
-
memset(mpext, 0, sizeof(*mpext));
mpext->data_seq = data_seq;
mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
- mpext->data_len = ret;
+ mpext->data_len = copy;
mpext->use_map = 1;
mpext->dsn64 = 1;

@@ -1380,18 +1397,18 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
mpext->dsn64);

if (zero_window_probe) {
- mptcp_subflow_ctx(ssk)->rel_write_seq += ret;
+ mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
mpext->frozen = 1;
if (READ_ONCE(msk->csum_enabled))
- mptcp_update_data_checksum(tail, ret);
+ mptcp_update_data_checksum(skb, copy);
tcp_push_pending_frames(ssk);
return 0;
}
out:
if (READ_ONCE(msk->csum_enabled))
- mptcp_update_data_checksum(tail, ret);
- mptcp_subflow_ctx(ssk)->rel_write_seq += ret;
- return ret;
+ mptcp_update_data_checksum(skb, copy);
+ mptcp_subflow_ctx(ssk)->rel_write_seq += copy;
+ return copy;
}

#define MPTCP_SEND_BURST_SIZE ((1 << 16) - \
--
2.35.1