Date: Tue, 22 Mar 2005 10:23:31 +0100
From: Ingo Molnar <mingo@elte.hu>
To: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [patch] Real-Time Preemption, -RT-2.6.12-rc1-V0.7.41-01
Message-ID: <20050322092331.GA21465@elte.hu>
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* Ingo Molnar <mingo@elte.hu> wrote:

> > Does the following help with the SMP problem?  This fix and the
> > earlier one make my old patch survive a few rounds of kernbench on a
> > 4-CPU x86 box. [...]
> 
> does not seem to fix my testbox (see the crash log below). [...]

seems to be a true SMP race: when i boot with 1 CPU it doesnt trigger,
the same kernel image and 2 CPUs triggers it on CPU#1. (CPU#0 is the
boot CPU) Note that the timing of the crash is not deterministic
(sometimes i get it during net startup, sometimes during ACPI startup),
but it always crashes within rcu_advance_callbacks().

one difference between your tests and mine is that your kernel is doing
_synchronize_kernel() from preempt-off sections (correct?), while my
kernel with PREEMPT_RT does it on preemptable sections.

	Ingo
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