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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: bwatson@kahuna.cag.cpqcorp.net, marcelo@conectiva.com.br,
        linux-kernel@vger.kernel.org, dhowells@redhat.com, hch@caldera.de
Subject: Re: [PATCH] 2.4.18-pre9, trylock for read/write semaphores 
In-Reply-To: Message from Alan Cox <alan@lxorguk.ukuu.org.uk> 
   of "Tue, 12 Feb 2002 23:29:29 GMT." <E16amMb-0003RQ-00@the-village.bc.nu> 
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Date: Wed, 13 Feb 2002 07:47:32 +0000
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From: David Howells <dhowells@redhat.com>
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> > +	new = old + RWSEM_ACTIVE_READ_BIAS;
> > +	if (cmpxchg(&sem->count, old, new) == old)
> > +		return 1;
> 
> cmpxchg isnt present on i386

This isn't actually relevant... <asm/rwsem.h> isn't actually used unless
CONFIG_RWSEM_GENERIC_SPINLOCK is turned off, which it isn't if the CPU type is
configured to "i386":

	[arch/i386/config.in]
	if [ "$CONFIG_M386" = "y" ]; then
	   define_bool CONFIG_X86_CMPXCHG n
	   define_bool CONFIG_X86_XADD n
	   define_int  CONFIG_X86_L1_CACHE_SHIFT 4
	   define_bool CONFIG_RWSEM_GENERIC_SPINLOCK y
	   define_bool CONFIG_RWSEM_XCHGADD_ALGORITHM n
	else
	   define_bool CONFIG_X86_WP_WORKS_OK y
	   define_bool CONFIG_X86_INVLPG y
	   define_bool CONFIG_X86_CMPXCHG y
	   define_bool CONFIG_X86_XADD y
	   define_bool CONFIG_X86_BSWAP y
	   define_bool CONFIG_X86_POPAD_OK y
	   define_bool CONFIG_RWSEM_GENERIC_SPINLOCK n
	   define_bool CONFIG_RWSEM_XCHGADD_ALGORITHM y
	fi

	[include/linux/rwsem.h]
	#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
	#include <linux/rwsem-spinlock.h> /* use a generic implementation */
	#else
	#include <asm/rwsem.h> /* use an arch-specific implementation */
	#endif

David
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