Re: xen-4.6: xenstored crashes during domain->interface access

[Ian Campbell <ian.campbell@citrix.com>]

On Thu, 2016-01-28 at 09:50 +0100, Stefan Bader wrote:
> On 26.01.2016 11:58, Stefan Bader wrote:
> > Hi,
> > 
> > while playing around with xen-4.6 I stumbled over an odd problem and am
> > wondering whether anybody has seen the same. A method to relatively
> > quickly
> > reproduce this for me seems to:
> > 
> > - Start one domU (PV or HVM does not seem to matter)
> > - Repeatedly call xenstore-ls a few times
> > 
> > I think I never got beyond 10 repeats when the xenstore-ls call
> > suddenly locks
> > up and xenstored crashes with a SIGBUS error. In the majority of cases
> > (I think
> > I saw one different), the crash happens while accessing conn->domain-
> > >interface
> > in tools/xenstore/xenstored_domain.c:domain_can_read().
> > Looking at the corefile produced by xenstored I now got at least one
> > case where
> > the pointer still matches the previously mapped value. Though I think I
> > had also
> > at least one run (with less debugging added) where it seemed to be
> > really wrong.
> > There is more info at [1] in case someone is interested.
> > 
> > I need to repeat a few more times to see how consistent the whole thing
> > is. Does
> > this happen for anybody else? Any advice what I should look at (in the
> > sense of
> > gathering better data)?
> 
> Just as an update and confirmation for Ian and Bastian: Debian testing is fine.
> I have not dug into the specifics but its not the Xen package side at all.
> Something in our 4.3 kernel causes this. Unfortunately without any hint in
> dmesg. But since we move to 4.4 soon and I cannot reproduce it with the pending
> 4.4 build it seems good enough to me.

Ah, this is probably fixed by 9c17d96500f78 "xen/gntdev: Grant maps should
not be subject to NUMA balancing" then.

Ian.