netdev - Re: [RFC PATCH v2 net-next 2/7] tcp: Merge tx_flags/tskey/txstamp_ack in tcp_collapse

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 19 Apr 2016 10:28:37 -0700
From:	Martin KaFai Lau <kafai@...com>
To:	Soheil Hassas Yeganeh <soheil@...gle.com>
CC:	<netdev@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Soheil Hassas Yeganeh <soheil.kdev@...il.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Kernel Team <kernel-team@...com>
Subject: Re: [RFC PATCH v2 net-next 2/7] tcp: Merge
 tx_flags/tskey/txstamp_ack in tcp_collapse_retrans

On Tue, Apr 19, 2016 at 01:32:14AM -0400, Soheil Hassas Yeganeh wrote:
> > +               TCP_SKB_CB(skb)->txstamp_ack =
> > +                       !!(shinfo->tx_flags & SKBTX_ACK_TSTAMP);
>
> Maybe we can skip a conditional jump here (because of !!), by simply
> using the cached bit in next_skb:
> TCP_SKB_CB(skb)->txstamp_ack = TCP_SKB_CB(next_skb)->txstamp_ack;
Recall the tx_flags are merged/combined (and so should be the txstamp_ack).
Would there be a case that TCP_SKB_CB(skb)->txstamp_ack is 1 and
TCP_SKB_CB(next_skb)->txstamp_ack is 0?

I can change it like the following which may help in showing the intention:
if (TCP_SKB_CB(next_skb)->txstamp_ack)
	TCP_SKB_CB(skb)->txstamp_ack = 1;

A bit off topic, I feel like the SKBTX_ACK_TSTAMP and txstamp_ack are sort
of redundant but I have not look into the details yet, so not completely
sure.  It wwould be a separate cleanup patch if it is the case.