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Date: Thu, 19 May 2011 23:15:00 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Yinghai Lu <yinghai@kernel.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [GIT PULL rcu/next] rcu commits for 2.6.40
Message-ID: <20110519211458.GG1956@nowhere>
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On Thu, May 19, 2011 at 12:51:26PM -0700, Yinghai Lu wrote:
> [   85.194797]   <idle>-0       0d... 85152953us : rcu_irq_enter: 1 49
> [   85.194808]   <idle>-0       0dN.. 85153081us : <stack trace>
> [   85.194809]  => rcu_irq_exit
> [   85.194810]  => irq_exit
> [   85.194811]  => smp_apic_timer_interrupt
> [   85.194812]  => apic_timer_interrupt
> [   85.194813]  => cpu_idle
> [   85.194813]  => rest_init
> [   85.194814]  => start_kernel
> [   85.194815]  => x86_64_start_reservations

So it's the dynticks_nesting going crazy. As if we had rcu_irq_enter()
without rcu_irq_exit().

I see you have CONFIG_DEBUG_LOCKING_API_SELFTESTS=y
and the locking api selftest is doing a strange thing: if we look
at HARDIRQ_ENTER(), it calls irq_enter(), but HARDIRQ_EXIT() only
calls __irq_exit(). Which means it lacks the rcu_irq_exit().

So, if I understood correctly the thing there, some selftests simulating
the hardirq context are unbalancing the rcu state.

Does that help if you unset CONFIG_DEBUG_LOCKING_API_SELFTESTS ?