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From: presotto@pla...
Subject: Kernel question: i386 test-and-set problem
Date: Thu, 20 Jul 2000 13:09:30 -0400

r->p is either 0 or a valid process number.  Therefore, the r->p
access shouldn't cause a crash.  We later check the p->r against r
under lock to make sure the process is still waiting on that
rendezvouz.  The worst the unlocked access should do is miss
a sleep which was in the process of happening.  That would have happened
even with the lock with a small delta in timing.

In v2 the lock was providing the coherence() that we put herein v3.
However, v2 also had deadlock problems twixt sleep and postnote
that v3 fixes.