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mptcp: rework mptcp_sendmsg_frag to accept optional dfrag
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This will simplify mptcp-level retransmission implementation
in the next patch. If dfrag is provided by the caller, skip
kernel space memory allocation and use data and metadata
provided by the dfrag itself.

Because a peer could ack data at TCP level but refrain from
sending mptcp-level ACKs, we could grow the mptcp socket
backlog indefinitely.

We should thus block mptcp_sendmsg until the peer has acked some of the
sent data.

In order to be able to do so, increment the mptcp socket wmem_queued
counter on memory allocation and decrement it when releasing the memory
on mptcp-level ack reception.

Because TCP performns sndbuf auto-tuning up to tcp_wmem_max[2], make
this the mptcp sk_sndbuf limit.

In the future we could add experiment with autotuning as TCP does in
tcp_sndbuf_expand().

v2 -> v3:
 - remove 'inline' in foo.c files (David S. Miller)

Co-developed-by: Florian Westphal <[email protected]>
Signed-off-by: Florian Westphal <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: Mat Martineau <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
Paolo Abeni authored and davem330 committed Mar 30, 2020
1 parent 7948f6c commit 3f8e0aa
Showing 1 changed file with 74 additions and 49 deletions.
123 changes: 74 additions & 49 deletions net/mptcp/protocol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -316,15 +316,15 @@ static struct sock *mptcp_subflow_recv_lookup(const struct mptcp_sock *msk)
return NULL;
}

static inline bool mptcp_skb_can_collapse_to(const struct mptcp_sock *msk,
const struct sk_buff *skb,
const struct mptcp_ext *mpext)
static bool mptcp_skb_can_collapse_to(u64 write_seq,
const struct sk_buff *skb,
const struct mptcp_ext *mpext)
{
if (!tcp_skb_can_collapse_to(skb))
return false;

/* can collapse only if MPTCP level sequence is in order */
return mpext && mpext->data_seq + mpext->data_len == msk->write_seq;
return mpext && mpext->data_seq + mpext->data_len == write_seq;
}

static bool mptcp_frag_can_collapse_to(const struct mptcp_sock *msk,
Expand Down Expand Up @@ -417,23 +417,28 @@ mptcp_carve_data_frag(const struct mptcp_sock *msk, struct page_frag *pfrag,
}

static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
struct msghdr *msg, long *timeo, int *pmss_now,
struct msghdr *msg, struct mptcp_data_frag *dfrag,
long *timeo, int *pmss_now,
int *ps_goal)
{
int mss_now, avail_size, size_goal, offset, ret, frag_truesize = 0;
bool dfrag_collapsed, can_collapse = false;
struct mptcp_sock *msk = mptcp_sk(sk);
struct mptcp_ext *mpext = NULL;
struct mptcp_data_frag *dfrag;
bool retransmission = !!dfrag;
struct sk_buff *skb, *tail;
struct page_frag *pfrag;
struct page *page;
u64 *write_seq;
size_t psize;

/* use the mptcp page cache so that we can easily move the data
* from one substream to another, but do per subflow memory accounting
* Note: pfrag is used only !retransmission, but the compiler if
* fooled into a warning if we don't init here
*/
pfrag = sk_page_frag(sk);
while (!mptcp_page_frag_refill(ssk, pfrag) ||
while ((!retransmission && !mptcp_page_frag_refill(ssk, pfrag)) ||
!mptcp_ext_cache_refill(msk)) {
ret = sk_stream_wait_memory(ssk, timeo);
if (ret)
Expand All @@ -447,6 +452,13 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
if (unlikely(__mptcp_needs_tcp_fallback(msk)))
return 0;
}
if (!retransmission) {
write_seq = &msk->write_seq;
page = pfrag->page;
} else {
write_seq = &dfrag->data_seq;
page = dfrag->page;
}

/* compute copy limit */
mss_now = tcp_send_mss(ssk, &size_goal, msg->msg_flags);
Expand All @@ -464,63 +476,74 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
* SSN association set here
*/
can_collapse = (size_goal - skb->len > 0) &&
mptcp_skb_can_collapse_to(msk, skb, mpext);
mptcp_skb_can_collapse_to(*write_seq, skb, mpext);
if (!can_collapse)
TCP_SKB_CB(skb)->eor = 1;
else
avail_size = size_goal - skb->len;
}

/* reuse tail pfrag, if possible, or carve a new one from the page
* allocator
*/
dfrag = mptcp_rtx_tail(sk);
offset = pfrag->offset;
dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag);
if (!dfrag_collapsed) {
dfrag = mptcp_carve_data_frag(msk, pfrag, offset);
if (!retransmission) {
/* reuse tail pfrag, if possible, or carve a new one from the
* page allocator
*/
dfrag = mptcp_rtx_tail(sk);
offset = pfrag->offset;
dfrag_collapsed = mptcp_frag_can_collapse_to(msk, pfrag, dfrag);
if (!dfrag_collapsed) {
dfrag = mptcp_carve_data_frag(msk, pfrag, offset);
offset = dfrag->offset;
frag_truesize = dfrag->overhead;
}
psize = min_t(size_t, pfrag->size - offset, avail_size);

/* Copy to page */
pr_debug("left=%zu", msg_data_left(msg));
psize = copy_page_from_iter(pfrag->page, offset,
min_t(size_t, msg_data_left(msg),
psize),
&msg->msg_iter);
pr_debug("left=%zu", msg_data_left(msg));
if (!psize)
return -EINVAL;

if (!sk_wmem_schedule(sk, psize + dfrag->overhead))
return -ENOMEM;
} else {
offset = dfrag->offset;
frag_truesize = dfrag->overhead;
psize = min_t(size_t, dfrag->data_len, avail_size);
}
psize = min_t(size_t, pfrag->size - offset, avail_size);

/* Copy to page */
pr_debug("left=%zu", msg_data_left(msg));
psize = copy_page_from_iter(pfrag->page, offset,
min_t(size_t, msg_data_left(msg), psize),
&msg->msg_iter);
pr_debug("left=%zu", msg_data_left(msg));
if (!psize)
return -EINVAL;

if (!sk_wmem_schedule(sk, psize + dfrag->overhead))
return -ENOMEM;

/* tell the TCP stack to delay the push so that we can safely
* access the skb after the sendpages call
*/
ret = do_tcp_sendpages(ssk, pfrag->page, offset, psize,
ret = do_tcp_sendpages(ssk, page, offset, psize,
msg->msg_flags | MSG_SENDPAGE_NOTLAST);
if (ret <= 0)
return ret;

frag_truesize += ret;
if (unlikely(ret < psize))
iov_iter_revert(&msg->msg_iter, psize - ret);
if (!retransmission) {
if (unlikely(ret < psize))
iov_iter_revert(&msg->msg_iter, psize - ret);

/* send successful, keep track of sent data for mptcp-level
* retransmission
*/
dfrag->data_len += ret;
if (!dfrag_collapsed) {
get_page(dfrag->page);
list_add_tail(&dfrag->list, &msk->rtx_queue);
}
/* send successful, keep track of sent data for mptcp-level
* retransmission
*/
dfrag->data_len += ret;
if (!dfrag_collapsed) {
get_page(dfrag->page);
list_add_tail(&dfrag->list, &msk->rtx_queue);
sk_wmem_queued_add(sk, frag_truesize);
} else {
sk_wmem_queued_add(sk, ret);
}

/* charge data on mptcp rtx queue to the master socket
* Note: we charge such data both to sk and ssk
*/
sk->sk_forward_alloc -= frag_truesize;
/* charge data on mptcp rtx queue to the master socket
* Note: we charge such data both to sk and ssk
*/
sk->sk_forward_alloc -= frag_truesize;
}

/* if the tail skb extension is still the cached one, collapsing
* really happened. Note: we can't check for 'same skb' as the sk_buff
Expand All @@ -539,7 +562,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
msk->cached_ext = NULL;

memset(mpext, 0, sizeof(*mpext));
mpext->data_seq = msk->write_seq;
mpext->data_seq = *write_seq;
mpext->subflow_seq = mptcp_subflow_ctx(ssk)->rel_write_seq;
mpext->data_len = ret;
mpext->use_map = 1;
Expand All @@ -550,8 +573,9 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
mpext->dsn64);

out:
pfrag->offset += frag_truesize;
msk->write_seq += ret;
if (!retransmission)
pfrag->offset += frag_truesize;
*write_seq += ret;
mptcp_subflow_ctx(ssk)->rel_write_seq += ret;

return ret;
Expand Down Expand Up @@ -663,7 +687,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)

lock_sock(ssk);
while (msg_data_left(msg)) {
ret = mptcp_sendmsg_frag(sk, ssk, msg, &timeo, &mss_now,
ret = mptcp_sendmsg_frag(sk, ssk, msg, NULL, &timeo, &mss_now,
&size_goal);
if (ret < 0)
break;
Expand Down Expand Up @@ -974,6 +998,7 @@ static int mptcp_init_sock(struct sock *sk)
return ret;

sk_sockets_allocated_inc(sk);
sk->sk_sndbuf = sock_net(sk)->ipv4.sysctl_tcp_wmem[2];

if (!mptcp_is_enabled(sock_net(sk)))
return -ENOPROTOOPT;
Expand Down

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