netdev - Re: ppp/pppoe, still panic 4.15.3 in ppp

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Date:   Fri, 2 Mar 2018 18:43:28 +0100
From:   Guillaume Nault <g.nault@...halink.fr>
To:     Denys Fedoryshchenko <nuclearcat@...learcat.com>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: ppp/pppoe, still panic 4.15.3 in ppp_push

On Thu, Mar 01, 2018 at 10:07:05PM +0200, Denys Fedoryshchenko wrote:
> On 2018-03-01 22:01, Guillaume Nault wrote:
> > diff --git a/drivers/net/ppp/ppp_generic.c
> > b/drivers/net/ppp/ppp_generic.c
> > index 255a5def56e9..2acf4b0eabd1 100644
> > --- a/drivers/net/ppp/ppp_generic.c
> > +++ b/drivers/net/ppp/ppp_generic.c
> > @@ -3161,6 +3161,15 @@ ppp_connect_channel(struct channel *pch, int
> > unit)
> >  		goto outl;
> > 
> >  	ppp_lock(ppp);
> > +	spin_lock_bh(&pch->downl);
> > +	if (!pch->chan) {
> > +		/* Don't connect unregistered channels */
> > +		ppp_unlock(ppp);
> > +		spin_unlock_bh(&pch->downl);

This is obviously wrong. It should have been
+		spin_unlock_bh(&pch->downl);
+		ppp_unlock(ppp);

Sorry, I shouldn't have hurried.
This is fixed in the official version.

> > +		ret = -ENOTCONN;
> > +		goto outl;
> > +	}
> > +	spin_unlock_bh(&pch->downl);
> >  	if (pch->file.hdrlen > ppp->file.hdrlen)
> >  		ppp->file.hdrlen = pch->file.hdrlen;
> >  	hdrlen = pch->file.hdrlen + 2;	/* for protocol bytes */
> Ok, i will try to test that at night.
> Thanks a lot! For me also problem solved anyway by removing unit-cache, just
> i think it's nice to have bug fixed :)
> 
I think this bug has been there forever, indeed it's good to have it fixed.
Thanks a lot for your help (and patience!).

FYI, if you see accel-ppp logs like
"ioctl(PPPIOCCONNECT): Transport endpoint is not connected", then that
means the patch prevented the scenario that was leading to the original
crash.

Out of curiosity, did unit-cache really bring performance improvements
on your workload?