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mptcp: do not shrink snd_nxt when recovering 

When recovering after a link failure, snd_nxt should not be set to a
lower value.  Else, update of snd_nxt is broken because:

  msk->snd_nxt += ret; (where ret is number of bytes sent)

assumes that snd_nxt always moves forward.
After reduction, its possible that snd_nxt update gets out of sync:
dfrag we just sent might have had a data sequence number even past
recovery_snd_nxt.

This change factors the common msk state update to a helper
and updates snd_nxt based on the current dfrag data sequence number.

The conditional is required for the recovery phase where we may
re-transmit old dfrags that are before current snd_nxt.

After this change, snd_nxt only moves forward and covers all in-sequence
data that was transmitted.

recovery_snd_nxt is retained to detect when recovery has completed.

Fixes: 1e1d9d6f11 ("mptcp: handle pending data on closed subflow")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Florian Westphal 2021-09-24 14:12:34 -07:00 committed by David S. Miller
parent 8765de69e7
commit 0d199e4363
2 changed files with 34 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
net/mptcp/options.c
View File

@ -1019,11 +1019,9 @@ static void ack_update_msk(struct mptcp_sock *msk,
old_snd_una = msk->snd_una;
new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
/* ACK for data not even sent yet and even above recovery bound? Ignore.*/
if (unlikely(after64(new_snd_una, snd_nxt))) {
if (!msk->recovery || after64(new_snd_una, msk->recovery_snd_nxt))
new_snd_una = old_snd_una;
}
/* ACK for data not even sent yet? Ignore.*/
if (unlikely(after64(new_snd_una, snd_nxt)))
new_snd_una = old_snd_una;
new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;

43
net/mptcp/protocol.c
View File

@ -1525,6 +1525,32 @@ static void mptcp_push_release(struct sock *sk, struct sock *ssk,
release_sock(ssk);
}
static void mptcp_update_post_push(struct mptcp_sock *msk,
struct mptcp_data_frag *dfrag,
u32 sent)
{
u64 snd_nxt_new = dfrag->data_seq;
dfrag->already_sent += sent;
msk->snd_burst -= sent;
msk->tx_pending_data -= sent;
snd_nxt_new += dfrag->already_sent;
/* snd_nxt_new can be smaller than snd_nxt in case mptcp
* is recovering after a failover. In that event, this re-sends
* old segments.
*
* Thus compute snd_nxt_new candidate based on
* the dfrag->data_seq that was sent and the data
* that has been handed to the subflow for transmission
* and skip update in case it was old dfrag.
*/
if (likely(after64(snd_nxt_new, msk->snd_nxt)))
msk->snd_nxt = snd_nxt_new;
}
void __mptcp_push_pending(struct sock *sk, unsigned int flags)
{
struct sock *prev_ssk = NULL, *ssk = NULL;
@ -1568,12 +1594,10 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
}
info.sent += ret;
dfrag->already_sent += ret;
msk->snd_nxt += ret;
msk->snd_burst -= ret;
msk->tx_pending_data -= ret;
copied += ret;
len -= ret;
mptcp_update_post_push(msk, dfrag, ret);
}
WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
}
@ -1626,13 +1650,11 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
goto out;
info.sent += ret;
dfrag->already_sent += ret;
msk->snd_nxt += ret;
msk->snd_burst -= ret;
msk->tx_pending_data -= ret;
copied += ret;
len -= ret;
first = false;
mptcp_update_post_push(msk, dfrag, ret);
}
WRITE_ONCE(msk->first_pending, mptcp_send_next(sk));
}
@ -2230,15 +2252,12 @@ bool __mptcp_retransmit_pending_data(struct sock *sk)
return false;
}
/* will accept ack for reijected data before re-sending them */
if (!msk->recovery || after64(msk->snd_nxt, msk->recovery_snd_nxt))
msk->recovery_snd_nxt = msk->snd_nxt;
msk->recovery_snd_nxt = msk->snd_nxt;
msk->recovery = true;
mptcp_data_unlock(sk);
msk->first_pending = rtx_head;
msk->tx_pending_data += msk->snd_nxt - rtx_head->data_seq;
msk->snd_nxt = rtx_head->data_seq;
msk->snd_burst = 0;
/* be sure to clear the "sent status" on all re-injected fragments */