linux-kernel - Re: preempt rcu bug on s390

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Message-ID: <20080209140711.GA16205@linux.vnet.ibm.com>
Date:	Sat, 9 Feb 2008 06:07:11 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Gautham R Shenoy <ego@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Steven Rostedt <srostedt@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: preempt rcu bug on s390

On Sat, Feb 09, 2008 at 12:34:35PM +0100, Heiko Carstens wrote:
> Using CONFIG_PREEMPT_RCU and CONFIG_NO_IDLE_HZ on s390 my system always
> gets stuck when running with more than one cpu.
> When booting with four cpus I get all four cpus caught withing cpu_idle
> and not advancing anymore. However there is the init process which is
> waitung for synchronize_rcu() to complete (lcrash output):
> 
> STACK TRACE FOR TASK: 0xf84d968 (swapper)
> 
>  STACK:
>  0 schedule+842 [0x36c956]
>  1 schedule_timeout+172 [0x36d0e4]
>  2 wait_for_common+204 [0x36c398]
>  3 synchronize_rcu+76 [0x567bc]
>  4 netlink_change_ngroups+150 [0x2b4302]
>  5 genl_register_mc_group+256 [0x2b6174]
>  6 genl_init+188 [0x534e44]
>  7 kernel_init+444 [0x518334]
>  8 kernel_thread_starter+6 [0x192a6]
> 
> If I change the code so that timer ticks won't be disabled everything
> runs fine. So my guess is that rcu_needs_cpu() doesn't do the right
> thing for the rcu preemptible case.
> 
> Kernel version is git head of today.
> 
> Any ideas?

Does this tree have http://lkml.org/lkml/2008/1/29/208 applied?

If not, could you please check it out?

						Thanx, Paul
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