linux-kernel - Re: Spinlocks: Factor our GENERIC_LOCKBREAK in order to avoid spin with irqs disable

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Date:	Fri, 9 May 2008 09:28:14 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Spinlocks: Factor our GENERIC_LOCKBREAK in order to avoid spin
 with irqs disable

On Fri, 9 May 2008, Ingo Molnar wrote:

> hm, there was some lockdep complication in this area. I guess we could 
> use the 'nice' variants too if their irq-enabling/disabling was properly 
> lockdep annotated and tracked by the irqflags machinery?

I thought that we already fall back to the functions that spin while 
having interrupts disabled if lockdep is on?

One issue: The BREAKLOCK value needs to be 1 in the fallback case 
otherwise we needlessly run atomic ops.

---
 kernel/spinlock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/kernel/spinlock.c
===================================================================
--- linux-2.6.orig/kernel/spinlock.c	2008-05-07 16:00:06.000000000 -0700
+++ linux-2.6/kernel/spinlock.c	2008-05-07 16:00:29.000000000 -0700
@@ -218,7 +218,7 @@ do {									\
 
 #else
 
-#define BREAKLOCK(lock)	0
+#define BREAKLOCK(lock)	1
 #define BREAKLOCK_ENABLE(lock)	do { } while (0)
 #define BREAKLOCK_DISABLE(lock) do { } while (0)
 
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