Re: [PATCH] CPU hotplug, smpboot: Fix crash in smpboot_thread_fn()

From: Thomas Gleixner
Date: Thu Apr 11 2013 - 04:11:16 EST


On Wed, 10 Apr 2013, Srivatsa S. Bhat wrote:

> Interestingly, in every single stack trace, the crashing task is the migration
> thread. Now, migration thread belongs to the highest priority stop_task sched
> class, and this particular sched class is very unique in the way it implements
> its internal sched class functions, and I suspect this has a lot of bearing
> on how functions like kthread_bind(), wake_up_process() etc react with it
> (by looking at how it implements its functions such as select_task_rq(),
> enqueue_task(), dequeue_task() etc).

I don't think that's relevant. The migration thread can only be woken
via try_to_wakeup and my previous patch which implements a separate
task state makes sure that it cannot be woken accidentaly by anything
else than unpark.

> But note that __kthread_bind() can wake up the task if the task is an RT
> task. So it can be called only when the CPU (to which we want to bind the task)

kthread_bind() does NOT wakeup anything. It merily sets the cpus
allowed ptr without further ado.


Thanks,

tglx
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