linux-kernel - Re: [PATCH bpf-next v8 1/3] net: Rename mono_delivery_time to tstamp

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Date: Tue, 28 May 2024 13:24:35 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: "Abhishek Chauhan (ABC)" <quic_abchauha@...cinc.com>, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Andrew Halaney <ahalaney@...hat.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Martin KaFai Lau <martin.lau@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 bpf <bpf@...r.kernel.org>
Cc: kernel@...cinc.com, 
 Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next v8 1/3] net: Rename mono_delivery_time to
 tstamp_type for scalabilty

Abhishek Chauhan (ABC) wrote:

> > +static inline void skb_set_delivery_type_by_clockid(struct sk_buff *skb,
> > +						    ktime_t kt, clockid_t clockid)
> > +{
> > +	u8 tstamp_type = SKB_CLOCK_REALTIME;
> > +
> > +	switch (clockid) {
> > +	case CLOCK_REALTIME:
> > +		break;
> > +	case CLOCK_MONOTONIC:
> > +		tstamp_type = SKB_CLOCK_MONOTONIC;
> > +		break;
> > +	default:
> 
> Willem and Martin, I was thinking we should remove this warn_on_once from below line. Some systems also use panic on warn. 
> So i think this might result in unnecessary crashes. 
> 
> Let me know what you think. 
> 
> Logs which are complaining. 
> https://syzkaller.appspot.com/x/log.txt?x=118c3ae8980000

I received reports too. Agreed that we need to fix these reports.

The alternative is to limit sk_clockid to supported ones, by failing
setsockopt SO_TXTIME on an unsupported clock.

That changes established ABI behavior. But I don't see how another
clock can be used in any realistic way anyway.

Putting it out there as an option. It's riskier, but in the end I
believe a better fix than just allowing this state to continue.

A third option would be to not fail the system call, but silently
fall back to CLOCK_REALTIME. Essentially what happens in the datapath
in skb_set_delivery_type_by_clockid now. That is surprising behavior,
we should not do that.