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

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Date:   Thu, 01 Mar 2018 22:07:05 +0200
From:   Denys Fedoryshchenko <nuclearcat@...learcat.com>
To:     Guillaume Nault <g.nault@...halink.fr>
Cc:     Cong Wang <xiyou.wangcong@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        netdev-owner@...r.kernel.org
Subject: Re: ppp/pppoe, still panic 4.15.3 in ppp_push



On 2018-03-01 22:01, Guillaume Nault wrote:
> On Tue, Feb 27, 2018 at 07:56:27PM +0100, Guillaume Nault wrote:
>> On Tue, Feb 27, 2018 at 12:58:55PM +0200, Denys Fedoryshchenko wrote:
>> > On 2018-02-23 12:07, Guillaume Nault wrote:
>> > > On Fri, Feb 23, 2018 at 11:41:43AM +0200, Denys Fedoryshchenko wrote:
>> > > > On 2018-02-23 11:38, Guillaume Nault wrote:
>> > > > > On Thu, Feb 22, 2018 at 08:51:19PM +0200, Denys Fedoryshchenko wrote:
>> > > > > > I'm using accel-ppp that has unit-cache option, i guess for
>> > > > > > "reusing" ppp
>> > > > > > interfaces (because creating a lot of interfaces on BRAS with 8k
>> > > > > > users quite
>> > > > > > expensive).
>> > > > > > Maybe it is somehow related and can be that scenario causing this bug?
>> > > > > >
>> > > > > Indeed, it'd be interesting to know if unit-cache is part of the
>> > > > > equation (if it's workable for you to disable it).
>> > > > Already did that and testing, unfortunately i had to disable KASAN
>> > > > and full
>> > > > refcount, as performance hit is too heavy for me. I will try to
>> > > > enable KASAN
>> > > > alone tomorrow.
>> > > >
>> > > Don't hesitate to post the result even if you can't afford enabling
>> > > KASAN.
>> > Till now 4 days and no reboots.
>> >
>> That unit-cache information was very useful. I can now reproduce the
>> issue and work on a fix.
>> 
> You can try the following patch.
> 
> Sorry for the delay, I'm a bit out of time these days.
> 
> 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);
> +		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 :)