On Thu, Aug 13, 2015 at 04:59:01PM -0400, Sasha Levin wrote:
> Seems to work fine now, thanks!
I've no clue how this doesn't also explode on actual hardware, that code
is convoluted, read and weep.
Ingo, please stick somewhere appropriate :-)
---
Subject: sched: Avoid trying to dequeue/enqueue the idle thread
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu Aug 13 23:09:29 CEST 2015
Sasha reports that his virtual machine tries to schedule the idle
thread since commit 6c37067e2786 ("sched: Change the
sched_class::set_cpus_allowed() calling context").
His trace shows this happening from idle_thread_get()->init_idle(),
which is the _second_ init_idle() invocation on that task_struct, the
first being done through idle_init()->fork_idle(). (this code is
insane...)
Because we call init_idle() twice in a row, its ->sched_class ==
&idle_sched_class and ->on_rq = TASK_ON_RQ_QUEUED. This means
do_set_cpus_allowed() thinks we're queued and will call dequeue_task(),
which is implemented with BUG() for the idle class, seeing how
dequeueing the idle task is a daft thing.
Aside of the whole insanity of calling init_idle() _twice_, change the
code to call set_cpus_allowed_common() instead as this is 'obviously'
before the idle task gets ran etc..
Fixes: 6c37067e2786 ("sched: Change the sched_class::set_cpus_allowed() calling context")
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Tested-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/sched/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4924,7 +4924,7 @@ void init_idle(struct task_struct *idle,
idle->state = TASK_RUNNING;
idle->se.exec_start = sched_clock();
- do_set_cpus_allowed(idle, cpumask_of(cpu));
+ set_cpus_allowed_common(idle, cpumask_of(cpu));
/*
* We're having a chicken and egg problem, even though we are
* holding rq->lock, the cpu isn't yet set to this cpu so the
--
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