Re: RT patches expose netdev race [was Re: [RFC] [patch 2/2] powerpc 2.6.21-rt1: fix kernel hang and/or panic

From: linas@austin.ibm.com (Linas Vepstas)
Date: Wed, 16 May 2007 19:18:02 -0500

Hi,

On Tue, May 15, 2007 at 08:09:02PM +1000, Benjamin Herrenschmidt wrote:

quoted

On Tue, 2007-05-15 at 17:47 +0900, Tsutomu OWA wrote:

quoted

  I encountered the following error when doing netperf from other machine 
to Celleb running RT kernel.  PREEPT_NONE kernel works just fine as well.

Hrm... sounds a bit weird. I wonder if there's a locking bug in the
driver in the first place.

Linas, what's your take ?

Heh. I almost deleted the entire email thread cause it
didn't say "spidernet" in the subject line. :-)
Seriously, I really almost did ....

Since this is a long email; let me put a summary up front:
I think the RT/premption patches are exposing some sort
of race in the ip header handling code. The rest of the 
note is forensics pointing to this.

skb->head should never ever be NULL.