From owner-freebsd-smp  Thu Mar 22 10: 4:16 2001
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To: Tony Finch <dot@dotat.at>
Cc: freebsd-smp@FreeBSD.ORG
Subject: Re: Locked data-structures and delayed writes. 
References: <E14g6vW-00077j-00@hand.dotat.at> 
In-Reply-To: <E14g6vW-00077j-00@hand.dotat.at> ; from Tony Finch <dot@dotat.at>  "Thu, 22 Mar 2001 15:23:02 GMT."
Date: Thu, 22 Mar 2001 20:05:04 +0200
From: Mark Murray <mark@grondar.za>
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> Anyway, the question at hand is what happens if two threads on
> different CPUs are accessing the same locked data structure when the
> CPU delays writes to RAM, i.e.
> 
> 	acquire_lock(s);
> 	modify(s);
> 	release_lock(s);
> 
> Things are very broken if the write can be delayed until after the
> lock is released. What prevents that?

"man atomic", and look at the "acquire" and "release" memory barriers.

M
-- 
Mark Murray
Warning: this .sig is umop ap!sdn

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