linux-kernel - Re: lockdep internal warning in linux-next

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Message-ID: <20080609083952.GA32746@elte.hu>
Date:	Mon, 9 Jun 2008 10:39:52 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: lockdep internal warning in linux-next


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> When I boot the 2-way using
> http://userweb.kernel.org/~akpm/config-vmm.txt

this is probably the same as the known problem fixed by the patch below.

	Ingo

----------------->
Subject: sched: sched_clock() lockdep fix
From: Ingo Molnar <mingo@...e.hu>
Date: Thu Jun 05 15:04:17 CEST 2008

Sitsofe Wheeler reported a lockdep warning and bisected it down to:

> commit c6531cce6e6e4b99bcda46b6268d6f2d9e30aea4
> Author: Ingo Molnar <mingo@...e.hu>
> Date:   Mon May 12 21:21:14 2008 +0200
>
>     sched: do not trace sched_clock

do not use raw irq flags in cpu_clock() as it causes lockdep to lose
track of the true state of the IRQ flag.

Reported-and-bisected-by: Sitsofe Wheeler <sitsofe@...oo.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -862,7 +862,7 @@ unsigned long long notrace cpu_clock(int
 	unsigned long long prev_cpu_time, time, delta_time;
 	unsigned long flags;
 
-	raw_local_irq_save(flags);
+	local_irq_save(flags);
 	prev_cpu_time = per_cpu(prev_cpu_time, cpu);
 	time = __cpu_clock(cpu) + per_cpu(time_offset, cpu);
 	delta_time = time-prev_cpu_time;
@@ -871,7 +871,7 @@ unsigned long long notrace cpu_clock(int
 		time = __sync_cpu_clock(time, cpu);
 		per_cpu(prev_cpu_time, cpu) = time;
 	}
-	raw_local_irq_restore(flags);
+	local_irq_restore(flags);
 
 	return time;
 }
--
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