From mboxrd@z Thu Jan  1 00:00:00 1970
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Re: [sources] 20070413: /rc/bin/cpurc.local
From: "Russ Cox" <rsc@swtch.com>
Date: Tue, 17 Apr 2007 01:21:16 -0400
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> Not to be overly annoying, but _is_ it possible that between the
> assignment and that test, p->mach is set, indicating another CPU took
> over? It just doesn't seem like m->readied is locked, at all; it seems
> like another CPU could pick it up in the middle.

Many things are possible.  m->readied is just a hint.
p->mach is just a hint unless you hold the scheduling lock.

That's why dequeueproc double-checks:
    All the accesses in the if condition are just fine --
    they happen without a lock but dequeueproc double-checks
    that p is okay to schedule.

Russ