Re: [PATCH] balance RT task resched only on runqueue

[Ingo Molnar <mingo@elte.hu>]

* Steven Rostedt <rostedt@goodmis.org> wrote:

> In the RT kernel we discovered a place that can reschedule a task 
> without holding the tasks runqueue lock.  This was caused by the RT 
> balancing code that pulls RT tasks to the current run queue and will 
> reschedule the current task.
> 
> There's a slight chance that the pulling of the RT tasks will release 
> the current runqueue's lock and retake it (in the 
> double_lock_balance). During this time that the runqueue is released, 
> the current task can migrate to another runqueue.
> 
> In the prio_changed_rt code, after the pull, if the current task is of 
> lesser priority than one of the RT tasks pulled, resched_task is 
> called on the current task. If the current task had migrated in that 
> small window, resched_task will be called without holding the runqueue 
> lock for the runqueue that the task is on.
> 
> This race condition also exists in the mainline kernel and this patch 
> adds a check to make sure the task hasn't migrated before calling 
> resched_task.

thanks Steve, applied.

	Ingo