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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sun, Jul 10, 2011 at 04:14:49PM -0700, Paul E. McKenney wrote:
> On Sun, Jul 10, 2011 at 10:50:48PM +0100, julie Sullivan wrote:
> > > Very cool!  Thank you very much for the testing --
.. snip..
> And here is what I am proposing sending upstream.  I have your Tested-by,

Hey Paul,

I am hitting a similar bug.
Starting udev Kernel Device Manager...
Starting Configure read-only root support...
[   79.942067] INFO: rcu_sched_state detected stalls on CPUs/tasks: { 0} 
(detected by 2, t=60002 jiffies)
[   79.942089] sending NMI to all CPUs:

when running a 3.0-rc6 under Xen as 32-bit guest (I don't see this issue
when running a 64-bit guest) and when I've more than two CPUs under the guest.

I've tried the patch below against 3.0-rc6 and it did not fix the issue.

I've also tried to use 3.0-rc3 as somewhere in thread one of the reporters 
mentioned
that it worked for me - but that did not help me.

The config is a Fedora Core based. The stack traces of the four CPUs look
as follow:

CPU0:
Call Trace:
  [<c04023a7>] hypercall_page+0x3a7  <--
  [<c0405ed5>] xen_safe_halt+0x12 
  [<c040ea08>] default_idle+0x5a 
  [<c04081a6>] cpu_idle+0x8e 
  [<c07da9a9>] rest_init+0x5d 
  [<c0a86788>] start_kernel+0x34d 
  [<c0a861c4>] unknown_bootoption 
  [<c0a860ba>] i386_start_kernel+0xa9 
  [<c0a895ce>] xen_start_kernel+0x55d 
  [<c04090b1>] sys_rt_sigreturn+0xb 

CPU1 and CPU2:
Call Trace:
  [<c04023a7>] hypercall_page+0x3a7  <--
  [<c0405ed5>] xen_safe_halt+0x12 
  [<c040ea08>] default_idle+0x5a 
  [<c04081a6>] cpu_idle+0x8e 
  [<c07e5419>] cpu_bringup_and_idle+0xd 

CPU3:
Call Trace:
  [<c042d0f2>] task_waking_fair+0x11  <--
  [<c0439a45>] try_to_wake_up+0xb2 
  [<c0439b0c>] default_wake_function+0x10 
  [<c042d4db>] __wake_up_common+0x3b 
  [<c042ea69>] complete+0x3e 
  [<c0455e14>] wakeme_after_rcu+0x10 
  [<c048fd58>] __rcu_process_callbacks+0x172 
  [<c049080f>] rcu_process_callbacks+0x20 
  [<c044567d>] __do_softirq+0xa2 
  [<c04455db>] __do_softirq 
  [<c040a52d>] do_softirq+0x5a 

The full config is http://darnok.org/xen/config-rcu-stall
The full bootup log is http://darnok.org/xen/log-rcu-stall

Any thoughts of what I ought to try? I don't know if there is some missing 
functionality
in the RCU patches to work under Xen.... Any older version of Linux kernel
you would like me to try?

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