linux-kernel - Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

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Message-ID: <20110712151550.GA3397@linux.vnet.ibm.com>
Date:	Tue, 12 Jul 2011 08:15:50 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	xen-devel@...ts.xensource.com,
	julie Sullivan <kernelmail.jms@...il.com>,
	linux-kernel@...r.kernel.org, chengxu@...ux.vnet.ibm.com,
	kulkarni.ravi4@...il.com
Subject: Re: PROBLEM: 3.0-rc kernels unbootable since -rc3

On Tue, Jul 12, 2011 at 07:49:36AM -0700, Paul E. McKenney wrote:
> On Tue, Jul 12, 2011 at 10:12:28AM -0400, Konrad Rzeszutek Wilk wrote:
> > > >   [<c042d0f5>] task_waking_fair+0x14  <--
> > > 
> > > Hmmm...  This is a 32-bit system, isn't it?
> > 
> > Yes. I ran this little loop:
> > 
> > #!/bin/bash
> > 
> > ID=`xl list | grep Fedora | awk '  { print $2}'`
> > 
> > rm -f cpu*.log
> > while (true) do
> > 	xl pause $ID
> > 	 /usr/lib64/xen/bin/xenctx -s /mnt/tmp/FC15-32/System.map-3.0.0-rc6-julie-tested-dirty -a $ID 0 >> cpu0.log
> > 	 /usr/lib64/xen/bin/xenctx -s /mnt/tmp/FC15-32/System.map-3.0.0-rc6-julie-tested-dirty -a $ID 1 >> cpu1.log
> > 	 /usr/lib64/xen/bin/xenctx -s /mnt/tmp/FC15-32/System.map-3.0.0-rc6-julie-tested-dirty -a $ID 2 >> cpu2.log
> > 	 /usr/lib64/xen/bin/xenctx -s /mnt/tmp/FC15-32/System.map-3.0.0-rc6-julie-tested-dirty -a $ID 3 >> cpu3.log
> > 	xl unpause $ID
> > done
> > 
> > To get an idea what the CPU is doing before it hits the task_waking_fair
> > and there isn't anything daming. Here are the logs:
> > 
> > http://darnok.org/xen/cpu1.log
> 
> OK, a fair amount of variety, then lots and lots of task_waking_fair(),
> so I still feel good about asking you for the following.

But...  But...  But...

Just how accurate are these stack traces?  For example, do you have
frame pointers enabled?  If not, could you please enable them?

The reason that I ask is that the wakeme_after_rcu() looks like it is
being invoked from softirq, which would be grossly illegal and could
cause any manner of misbehavior.  Did someone put a synchronize_rcu()
into an RCU callback or something?  Or did I do something really really
braindead inside the RCU implementation?

(I am looking into this last question, but would appreciate any and all
help with the other questions!)

							Thanx, Paul
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