Re: [PATCH] Fix RCU race in access of nohz_cpu_mask

[David S. Miller]

From: Andrew Morton <akpm@xxxxxxxx>
Date: Sun, 11 Dec 2005 20:32:26 -0800

> So foo_mb() in preemptible code is potentially buggy.
> 
> I guess we assume that a context switch accidentally did enough of the
> right types of barriers for things to work OK.

A trap ought to flush all memory operations.

There are some incredibly difficult memory error handling cases if the
cpu does not synchronize all pending memory operations when a trap
occurs.

Failing that, yes, to be absolutely safe we'd need to have some
explicit memory barrier in the context switch.
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