On (Wed) 13 Aug 2014 [06:00:49], Paul E. McKenney wrote:
> On Wed, Aug 13, 2014 at 11:14:39AM +0530, Amit Shah wrote:
> > On (Tue) 12 Aug 2014 [14:41:51], Paul E. McKenney wrote:
> > > On Tue, Aug 12, 2014 at 02:39:36PM -0700, Paul E. McKenney wrote:
> > > > On Tue, Aug 12, 2014 at 09:06:21AM -0700, Paul E. McKenney wrote:
> > > > > On Tue, Aug 12, 2014 at 11:03:21AM +0530, Amit Shah wrote:
> > > >
> > > > [ . . . ]
> > > >
> > > > > > I know of only virtio-console doing this (via userspace only,
> > > > > > though).
> > > > >
> > > > > As in userspace within the guest? That would not work. The userspace
> > > > > that the qemu is running in might. There is a way to extract ftrace
> > > > > info
> > > > > from crash dumps, so one approach would be "sendkey alt-sysrq-c", then
> > > > > pull the buffer from the resulting dump. For all I know, there might
> > > > > also
> > > > > be some script that uses the qemu "x" command to get at the ftrace
> > > > > buffer.
> > > > >
> > > > > Again, I cannot reproduce this, and I have been through the code
> > > > > several
> > > > > times over the past few days, and am not seeing it. I could start
> > > > > sending you random diagnostic patches, but it would be much better if
> > > > > we could get the trace data from the failure.
> >
> > I think the only recourse I now have is to dump the guest state from
> > qemu, and attempt to find the ftrace buffers by poking pages and
> > finding some ftrace-like struct... and then dumping the buffers.
>
> The data exists in the qemu guest state, so it would be good to have
> it one way or another. My current (perhaps self-serving) guess is that
> you have come up with a way to trick qemu into dropping IPIs.
I didn't get around to doing this yet; will get to it next week.
In the meantime, I tried this on RHEL6 (with RHEL6 qemu and gcc and
seabios), and that exhibits the problem similarly with my .config.
<snip>
> > > +
> > > return true;
> >
> > I have return 1; here.
> >
> > I'm on linux.git, c8d6637d0497d62093dbba0694c7b3a80b79bfe1.
>
> I am working on top of my -rcu tree, which contains the fix from "1" to
> "true" compared to current mainline. So this will resolve itself, and
> you should be OK fixing up conflict in either direction.
Yep, I did do that. Just noted here that the hunk didn't directly
apply.
Thanks,
Amit
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