linux-kernel - RE: Uses for memory barriers

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Message-ID: <MDEHLPKNGKAHNMBLJOLKMEGHOEAB.davids@webmaster.com>
Date:	Thu, 7 Sep 2006 22:52:32 -0700
From:	"David Schwartz" <davids@...master.com>
To:	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: RE: Uses for memory barriers


> Am I correct?  Or are there some easily-explained situations where mb()
> really should be used for inter-CPU synchronization?

	Consider when one CPU does the following:

while(!spinlock_acquire()) relax();
x=shared_value_protected_by_spinlock;

	We need to make sure we do not *read* the protected values (say due to
prefetching) before other CPUs see our write that locks the spinlock.

	DS


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