linux-kernel - [tip:sched/core] cpu: Remove incorrect BUG

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Date:	Tue, 23 Nov 2010 10:22:54 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, oleg@...hat.com, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:sched/core] cpu: Remove incorrect BUG_ON

Commit-ID:  51a96c77815e7f139892a6e9c8275a50e9baebdf
Gitweb:     http://git.kernel.org/tip/51a96c77815e7f139892a6e9c8275a50e9baebdf
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Fri, 19 Nov 2010 20:37:53 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 23 Nov 2010 10:29:08 +0100

cpu: Remove incorrect BUG_ON

Oleg mentioned that there is no actual guarantee the dying cpu's
migration thread is actually finished running when we get there, so
replace the BUG_ON() with a spinloop waiting for it.

Reported-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/cpu.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 3945066..cb7a1ef 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -249,8 +249,11 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 	 * The migration_call() CPU_DYING callback will have removed all
 	 * runnable tasks from the cpu, there's only the idle task left now
 	 * that the migration thread is done doing the stop_machine thing.
+	 *
+	 * Wait for the stop thread to go away.
 	 */
-	BUG_ON(!idle_cpu(cpu));
+	while (!idle_cpu(cpu))
+		cpu_relax();
 
 	/* This actually kills the CPU. */
 	__cpu_die(cpu);
--
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