netdev - Re: [PATCH net-next 1/3] net-timestamp: add strict check when setting tx flags

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Message-ID: <CAL+tcoBMXtQ_TbjKmO5CazL5zu1dDBBB+enckkM9+0ojF3qutQ@mail.gmail.com>
Date: Mon, 30 Sep 2024 20:42:27 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org, 
	pabeni@...hat.com, dsahern@...nel.org, shuah@...nel.org, willemb@...gle.com, 
	linux-kselftest@...r.kernel.org, netdev@...r.kernel.org, 
	Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next 1/3] net-timestamp: add strict check when setting
 tx flags

On Mon, Sep 30, 2024 at 7:49 PM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > On Mon, Sep 30, 2024 at 6:39 PM Willem de Bruijn
> > <willemdebruijn.kernel@...il.com> wrote:
> > >
> > > Jason Xing wrote:
> > > > From: Jason Xing <kernelxing@...cent.com>
> > > >
> > > > Even though this case is unlikely to happen, we have to avoid such
> > > > a case occurring at an earlier point: the sk_rmem_alloc could get
> > > > increased because of inserting more and more skbs into the errqueue
> > > > when calling __skb_complete_tx_timestamp(). This bad case would stop
> > > > the socket transmitting soon.
> > >
> > > It is up to the application to read from the error queue frequently
> > > enough and/or increase SO_RCVBUF.
> >
> > Sure thing. If we test it without setting SOF_TIMESTAMPING_SOFTWARE on
> > the loopback, it will soon stop. That's the reason why I tried to add
> > the restriction just in case.
>
> I don't follow at all.
>
> That bit does not affect the core issue: that the application is not
> clearing its error queue quickly enough.
>
> > >
> > > > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > > > ---
> > > >  net/core/sock.c | 4 ++++
> > > >  1 file changed, 4 insertions(+)
> > > >
> > > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > > index fe87f9bd8f16..4bddd6f62e4f 100644
> > > > --- a/net/core/sock.c
> > > > +++ b/net/core/sock.c
> > > > @@ -905,6 +905,10 @@ int sock_set_timestamping(struct sock *sk, int optname,
> > > >       if (val & ~SOF_TIMESTAMPING_MASK)
> > > >               return -EINVAL;
> > > >
> > > > +     if (val & SOF_TIMESTAMPING_TX_RECORD_MASK &&
> > > > +         !(val & SOF_TIMESTAMPING_SOFTWARE))
> > > > +             return -EINVAL;
> > > > +
> > >
> > > This breaks hardware timestamping
> >
> > Yes, and sorry about that. I'll fix this.
>
> As is I don't understand the purpose of this patch. Please do not
> just resubmit with a change, but explain the problem and suggested
> solution first.
>

I will drop this patch because I just tested with my program in the
local machine and found there is one mistake I made about calculating
the diff between those two . Sorry for the noise.

Well, I only need to send a V2 patch of patch [3/3] in the next few days.

BTW, please allow me to ask one question unrelated to this patch
again. I do wonder: if we batch the recv skbs from the errqueue when
calling tcp_recvmsg() -> inet_recv_error(), it could break users,
right?

Thanks,
Jason