[tip:sched/core] cpu: Remove incorrect BUG_ON

tip-bot for Peter Zijlstra
2010-11-23T10:23:27Z

Commit-ID: 51a96c77815e7f139892a6e9c8275a50e9baebdf
Gitweb: http://git.kernel.org/tip/51a96c77815e7f139892a6e9c8275a50e9baebdf
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 19 Nov 2010 20:37:53 +0100
Committer: Ingo Molnar <mingo@elte.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@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.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);