Re: sky2 panic in 2.6.32.1 under load

[Michael Breuer]

On 12/24/2009 5:21 PM, Stephen Hemminger wrote:
> On Thu, 24 Dec 2009 11:28:57 -0500
> Daniel Hazelton<dhazelton@xxxxxxxxx>  wrote:
>
>    
> > On Thursday 24 December 2009 11:03:56 am Berck Nash wrote:
> >      
> > > Andrew Morton wrote:
> > >        
> > > > On Mon, 21 Dec 2009 16:52:10 -0700 "Berck E. Nash"<flyboy@xxxxxxxxx>
> > > >          
> > wrote:
> >      
> > > > > Since 2.6.32, I've been getting kernel panics under heavy network load
> > > > > (bittorrent usage).
> > > > >            
> > > > Let's cc the right list and developer.
> > > >
> > > > This is a 2.6.31->2.6.32 regression?
> > > >          
> > > I believe so.  Since it's intermittent and difficult to reproduce, it's
> > > possible (but unlikely) that I simply never triggered it under 2.6.31.
> > >        
> > This is far from new. I have seen this under 2.6.27 when at least one botnet
> > has been pointed at a server of mine and told to gain access. It has happened
> > four times in the last six to eight months - and I have no easy way to capture
> > the logs. But the oops that was posted looks very, very similar to what I've
> > seen.
> >
> > It's always an allocation error in the transmit path that leads to the panic.
> > Because this is a production machine that I do not have a way to take down and
> > do testing with I've not reported the problem before.
> >
> >      
> Even though I wrote/maintain the sky driver, I don't work for SysKonnect, and
> only have access to a limited set of information:
> the technical manuals (under NDA), and the vendor sk98lin driver. The sky2 driver
> imitates the receiver timeout of the sk98lin driver; other people have told me
> that the FIFO hardware implementation is buggy and when it gets full, it gets
> stuck. Probably the equivalent of a software FIFO where the developer forgets to
> reserve a slot so that head == tail can mean both empty and full!
>
> The workaround with a timer is prone to errors when traffic keeps going, also
> the vendor doesn't really provide clear instructions on how to unlock it. I do
> not have access to the hardware errata describing the problem. If I did a more
> minimal solution would be possible.
>
> The easiest advice is avoid sky2 chips with FIFO for any heavy traffic, the next
> advice is make sure receive flow control is enabled so that receiver doesn't
> get overrun. If tx timeouts are an issue use a rate limiter like TBF. Do not use
> the chip with 10 or 100 mbit since the transmitter is more prone to get overrun.
>    
For this particular issue, I'm only seeing problems when running at 1000 
mbit. 100 appears stable.
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