[PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

[PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

[zhenggy]

Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
multiple segments") fix some DSACK accounting for multiple segments.
In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
for tp->undo_retrans accounting.

Signed-off-by: zhenggy <zhenggy@chinatelecom.cn>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3f7bd7a..141e85e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1346,7 +1346,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
 	if (dup_sack && (sacked & TCPCB_RETRANS)) {
 		if (tp->undo_marker && tp->undo_retrans > 0 &&
 		    after(end_seq, tp->undo_marker))
-			tp->undo_retrans--;
+			tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
 		if ((sacked & TCPCB_SACKED_ACKED) &&
 		    before(start_seq, state->reord))
 				state->reord = start_seq;
-- 
1.8.3.1

Re: [PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

[Neal Cardwell]

On Thu, Sep 9, 2021 at 6:34 AM zhenggy <zhenggy@chinatelecom.cn> wrote:
>
> Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
> multiple segments") fix some DSACK accounting for multiple segments.
> In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
> for tp->undo_retrans accounting.
>
> Signed-off-by: zhenggy <zhenggy@chinatelecom.cn>
> ---
>  net/ipv4/tcp_input.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 3f7bd7a..141e85e 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -1346,7 +1346,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
>         if (dup_sack && (sacked & TCPCB_RETRANS)) {
>                 if (tp->undo_marker && tp->undo_retrans > 0 &&
>                     after(end_seq, tp->undo_marker))
> -                       tp->undo_retrans--;
> +                       tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
>                 if ((sacked & TCPCB_SACKED_ACKED) &&
>                     before(start_seq, state->reord))
>                                 state->reord = start_seq;
> --

Thanks for the fix!

I think it would be useful to have a Fixes: footer to help maintainers
know how far back to backport the fix.

I think an appropriate fixes footer might be the following:

Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")

Before that commit, the assumption underlying the tp->undo_retrans--
seems correct, AFAICT.

thanks,
neal

Re: [PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

[Neal Cardwell]

On Thu, Sep 9, 2021 at 9:38 AM Neal Cardwell <ncardwell@google.com> wrote:
>
> On Thu, Sep 9, 2021 at 6:34 AM zhenggy <zhenggy@chinatelecom.cn> wrote:
> >
> > Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
> > multiple segments") fix some DSACK accounting for multiple segments.
> > In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
> > for tp->undo_retrans accounting.
> >
> > Signed-off-by: zhenggy <zhenggy@chinatelecom.cn>

Another nit: in the commit title, rather than "net":

  net: fix tp->undo_retrans accounting in tcp_sacktag_one()

...I would suggest the more specific "tcp", which is more typical for
commits fixing tcp*.c files:

  tcp: fix tp->undo_retrans accounting in tcp_sacktag_one()

thanks,
neal

Re: [PATCH] net: fix tp->undo_retrans accounting in tcp_sacktag_one()

[zhenggy]

Hi，Neal：

Thanks very much for your checking, I will send a v2 patch to make it.

在 2021/9/9 21:38, Neal Cardwell 写道:
> On Thu, Sep 9, 2021 at 6:34 AM zhenggy <zhenggy@chinatelecom.cn> wrote:
>>
>> Commit a71d77e6be1e ("tcp: fix segment accounting when DSACK range covers
>> multiple segments") fix some DSACK accounting for multiple segments.
>> In tcp_sacktag_one(), we should also use the actual DSACK rang(pcount)
>> for tp->undo_retrans accounting.
>>
>> Signed-off-by: zhenggy <zhenggy@chinatelecom.cn>
>> ---
>>  net/ipv4/tcp_input.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index 3f7bd7a..141e85e 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -1346,7 +1346,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
>>         if (dup_sack && (sacked & TCPCB_RETRANS)) {
>>                 if (tp->undo_marker && tp->undo_retrans > 0 &&
>>                     after(end_seq, tp->undo_marker))
>> -                       tp->undo_retrans--;
>> +                       tp->undo_retrans = max_t(int, 0, tp->undo_retrans - pcount);
>>                 if ((sacked & TCPCB_SACKED_ACKED) &&
>>                     before(start_seq, state->reord))
>>                                 state->reord = start_seq;
>> --
> 
> Thanks for the fix!
> 
> I think it would be useful to have a Fixes: footer to help maintainers
> know how far back to backport the fix.
> 
> I think an appropriate fixes footer might be the following:
> 
> Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time")
> 
> Before that commit, the assumption underlying the tp->undo_retrans--
> seems correct, AFAICT.
> 
> thanks,
> neal
>