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From: Bjorn Helgaas <bjorn.helgaas@hp.com>
To: linux-kernel@vger.kernel.org
Subject: [PATCH] active_load_balance() deadlock
Date: Tue, 1 Jun 2004 14:09:54 -0600
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Cc: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@osdl.org>
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active_load_balance() looks susceptible to deadlock when busiest==rq.
Without the following patch, my 128-way box deadlocks consistently
during boot-time driver init.

===== kernel/sched.c 1.304 vs edited =====
--- 1.304/kernel/sched.c	2004-05-27 02:26:55 -06:00
+++ edited/kernel/sched.c	2004-05-31 12:03:32 -06:00
@@ -1847,6 +1847,8 @@
  		}
 
 		rq = cpu_rq(push_cpu);
+		if (busiest == rq)
+			goto next_group;
 		double_lock_balance(busiest, rq);
 		move_tasks(rq, push_cpu, busiest, 1, sd, IDLE);
 		spin_unlock(&rq->lock);