From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning
Date: Wed, 7 Jan 2009 15:19:23 -0800 (PST)
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Cc: Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	paulmck@linux.vnet.ibm.com, Gregory Haskins <ghaskins@novell.com>,
	Ingo Molnar <mingo@elte.hu>, Matthew Wilcox <matthew@wil.cx>,
	Andi Kleen <andi@firstfloor.org>,
	Chris Mason <chris.mason@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-btrfs <linux-btrfs@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Nick Piggin <npiggin@suse.de>,
	Peter Morreale <pmorreale@novell.com>,
	Sven Dietrich <SDietrich@novell.com>
To: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
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On Wed, 7 Jan 2009, Dave Kleikamp wrote:
> 
> Do you need to even do that if CONFIG_DEBUG_PAGEALLOC is unset?

No.

> Something like:
> 
> #ifdef CONFIG_DEBUG_PAGEALLOC
>                 /*
>                  * Need to access the cpu field knowing that
>                  * DEBUG_PAGEALLOC could have unmapped it if
>                  * the mutex owner just released it and exited.
>                  */
>                 if (probe_kernel_address(&thread->cpu, cpu))
>                         break;
> #else
> 		cpu = thread->cpu;
> #endif

yes. That would work fine.

			Linus