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From: Keith Owens <kaos@ocs.com.au>
To: Rusty Russell <rusty@rustcorp.com.au>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [DOCUMENTATION] Revised Unreliable Kernel Locking Guide 
In-reply-to: Your message of "Fri, 12 Dec 2003 15:44:01 -0000."
             <20031212154401.GA10584@redhat.com> 
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Date: Sat, 13 Dec 2003 03:25:52 +1100
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On Fri, 12 Dec 2003 15:44:01 +0000, 
Dave Jones <davej@redhat.com> wrote:
> Might be worth mentioning in the Per-CPU data section that code doing
>operations on CPU registers (MSRs and the like) needs to be protected
>by an explicit preempt_disable() / preempt_enable() pair if it's doing
>operations that it expects to run on a specific CPU.

Also calls to smp_call_function() need to be wrapped in preempt_disable,
plus any work that is done on the current cpu before/after calling a
function on the other cpus.  Lack of preempt disable could result in
the operation being done twice on one cpu and not at all on another.