Re: kernel BUG at drivers/xen/grant-table.c:923!

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

On Fri, 2015-04-17 at 11:45 +0100, Wei Liu wrote:
> On Fri, Apr 17, 2015 at 11:28:39AM +0100, Ian Campbell wrote:
> > (Was Re: [osstest test] 50423: regressions - FAIL)
> > 
> > This cropped up in an osstest flight (the results only go to Ian and I).
> > 
> > On Fri, 2015-04-17 at 11:10 +0100, Ian Campbell wrote:
> > > On Thu, 2015-04-16 at 21:36 +0000, osstest service user wrote:
> > > > flight 50423 osstest real [real]
> > > > http://logs.test-lab.xenproject.org/osstest/logs/50423/
> > > > 
> > > > Regressions :-(
> > > > 
> > > > Tests which did not succeed and are blocking,
> > > > including tests which could not be run:
> > > >  test-armhf-armhf-xl          15 guest-start/debian.repeat fail REGR. vs. 50331
> > > 
> > > 
> > > Looks to have been a real issue:
> > > 
> > > http://logs.test-lab.xenproject.org/osstest/logs/50423/test-armhf-armhf-xl/serial-cubietruck-gleizes.log
> > > Apr 14 19:01:21.834851 [ 1229.470934] ------------[ cut here ]------------
> > > Apr 14 19:01:22.445308 [ 1229.471001] kernel BUG at drivers/xen/grant-table.c:923!
> > 
> > This seems familiar, anyone remember it? (CCing ARM, netback and generic
> > Linux maintainers).
> > 
> > I had a look over
> > 
> > $ git log v3.16..origin/master -- drivers/net/xen-netback/ drivers/xen/ arch/*/xen
> > 
> > and nothing jumped out at me.
> > 
> > The new tests under flight include running tcpdump for the duration of
> > the migration. I wonder if that might have exposed the problem?
> > 
> > This is ARM for which osstest uses a 3.16 based kernel compared with x86
> > which is still on 3.14. That might explain why this was only seen on arm
> > (if tcpdump triggered it) or it might just be a very rare occurrence.
> > 
> 
> I've never seen this before. If I'm not mistaken this is referring to 
> 
>  918 void gnttab_batch_copy(struct gnttab_copy *batch, unsigned count)
>  919 {
>  920         struct gnttab_copy *op;
>  921
>  922         if (HYPERVISOR_grant_table_op(GNTTABOP_copy, batch, count))
>  923                 BUG();
>  924         for (op = batch; op < batch + count; op++)
>  925                 if (op->status == GNTST_eagain)
>  926                         gnttab_retry_eagain_gop(GNTTABOP_copy, op,
>  927                                                 &op->status, __func__);
>  928 }
> 
> Grant table op hypercall returns an error.
> 
> Would be useful to know what the actually error is.

Based on r0 I think -EFAULT.

Ian.