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ref: bd49212b467c60d6d5e4e2eefc13ec88012ec785
parent: e619a03c28a1bc979faeaa2853c58f94b5c3c5ad
author: cinap_lenrek <[email protected]>
date: Mon Sep 17 20:53:05 EDT 2018

kernel: fix livelock in rebalance (thanks Richard Miller)

Once a second rebalance() is called on cpu0 to adjust priorities,
so cpu-bound processes won't lock others out.  However it was only
adjusting processes which were running on cpu0.  This was observed
to lead to livelock, eg when a higher-priority process spin-waits
for a lock held by a lower priority one.

--- a/sys/src/9/port/proc.c

+++ b/sys/src/9/port/proc.c

@@ -478,8 +478,6 @@

 		p = rq->head;

 		if(p == nil)

 			continue;

-		if(p->mp != MACHP(m->machno))

-			continue;

 		if(pri == p->basepri)

 			continue;

 		updatecpu(p);