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[Xen-devel] Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

To: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: PROBLEM: 3.0-rc kernels unbootable since -rc3
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Tue, 12 Jul 2011 15:07:56 -0400
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, peterz@xxxxxxxxxxxxx, julie Sullivan <kernelmail.jms@xxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, chengxu@xxxxxxxxxxxxxxxxxx
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> > > Disabling CONFIG_NO_HZ would be an interesting test case.
> > 
> > Hadn't done that yet. Compiling a kernel with "# CONFIG_NO_HZ is not set"
> > right now.

Log: http://darnok.org/xen/loop_cnt-extra-patch-no-hz-disabled.log
Patch: http://darnok.org/xen/loop_cnt-extra-patch-no-hz-disabled.patch

> > > > > But the loop in task_waking_fair() looks like the most prominent 
> > > > > smoking
> > > > > gun at the moment.
> > > 
> > > And could you also please try out the patch that I posted earlier?
> > 
> > With the previous patch and the .. this is getting confusing. With this 
> > patch:
> > http://darnok.org/xen/loop_cnt-extra.patch
> That is indeed the patch I intended.

> > I get this output: http://darnok.org/xen/log.loop_cnt-extra-patch (one guest
> > with 4 VCPUS) and http://darnok.org/xen/loop_cnt-extra-patch.log (the guest 
> > with 16 VCPUs)
> OK, so the infinite loop in task_waking_fair() happens even if RCU callbacks
> are deferred until after the scheduler is fully initialized.  Sounds like
> one for the scheduler guys.  ;-)

Yikes. Well, in the meantime let me check the IPI part and see if there is 
busted that could trigger softirq to be invoked directly.

And also compile the kernel with the CONFIG_RCU_PROVE_LOCKING with some extra
git tree you pointed me to.
>                                                       Thanx, Paul

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