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tcp: let tcp_mtu_probe() build headless packets 

tcp_mtu_probe() is still copying payload from skbs in the write queue,
using skb_copy_bits(), ignoring potential errors.

Modern TCP stack wants to only deal with payload found in page frags,
as this is a prereq for TCPDirect (host stack might not have access
to the payload)

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230607214113.1992947-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2023-06-07 21:41:13 +00:00 committed by Jakub Kicinski
parent f84ad5cffd
commit 736013292e
1 changed files with 58 additions and 2 deletions
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60
net/ipv4/tcp_output.c
View File

@ -2319,6 +2319,57 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len)
return true;
}
static int tcp_clone_payload(struct sock *sk, struct sk_buff *to,
int probe_size)
{
skb_frag_t *lastfrag = NULL, *fragto = skb_shinfo(to)->frags;
int i, todo, len = 0, nr_frags = 0;
const struct sk_buff *skb;
if (!sk_wmem_schedule(sk, to->truesize + probe_size))
return -ENOMEM;
skb_queue_walk(&sk->sk_write_queue, skb) {
const skb_frag_t *fragfrom = skb_shinfo(skb)->frags;
if (skb_headlen(skb))
return -EINVAL;
for (i = 0; i < skb_shinfo(skb)->nr_frags; i++, fragfrom++) {
if (len >= probe_size)
goto commit;
todo = min_t(int, skb_frag_size(fragfrom),
probe_size - len);
len += todo;
if (lastfrag &&
skb_frag_page(fragfrom) == skb_frag_page(lastfrag) &&
skb_frag_off(fragfrom) == skb_frag_off(lastfrag) +
skb_frag_size(lastfrag)) {
skb_frag_size_add(lastfrag, todo);
continue;
}
if (unlikely(nr_frags == MAX_SKB_FRAGS))
return -E2BIG;
skb_frag_page_copy(fragto, fragfrom);
skb_frag_off_copy(fragto, fragfrom);
skb_frag_size_set(fragto, todo);
nr_frags++;
lastfrag = fragto++;
}
}
commit:
WARN_ON_ONCE(len != probe_size);
for (i = 0; i < nr_frags; i++)
skb_frag_ref(to, i);
skb_shinfo(to)->nr_frags = nr_frags;
to->truesize += probe_size;
to->len += probe_size;
to->data_len += probe_size;
__skb_header_release(to);
return 0;
}
/* Create a new MTU probe if we are ready.
* MTU probe is regularly attempting to increase the path MTU by
* deliberately sending larger packets. This discovers routing
@ -2395,9 +2446,15 @@ static int tcp_mtu_probe(struct sock *sk)
return -1;
/* We're allowed to probe. Build it now. */
nskb = tcp_stream_alloc_skb(sk, probe_size, GFP_ATOMIC, false);
nskb = tcp_stream_alloc_skb(sk, 0, GFP_ATOMIC, false);
if (!nskb)
return -1;
/* build the payload, and be prepared to abort if this fails. */
if (tcp_clone_payload(sk, nskb, probe_size)) {
consume_skb(nskb);
return -1;
}
sk_wmem_queued_add(sk, nskb->truesize);
sk_mem_charge(sk, nskb->truesize);
@ -2415,7 +2472,6 @@ static int tcp_mtu_probe(struct sock *sk)
len = 0;
tcp_for_write_queue_from_safe(skb, next, sk) {
copy = min_t(int, skb->len, probe_size - len);
skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
if (skb->len <= copy) {
/* We've eaten all the data from this skb.