Re: Possible lock-less list race in scheduler_ipi()

[Steven Rostedt]

On Fri, 6 Mar 2015 19:39:44 +0000 (UTC)
Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:

ask concurrently with the llist iteration within sched_ttwu_pending().
> 
> AFAIU, ttwu_queue_remote() is called from ttwu_queue() without holding
> the rq lock. So I'm wondering what prevents corruption of the wake_list
> in this situation.

I guess if it is on the wake_list, then the task's state is already
RUNNING. Any other task can switch a task's state to RUNNING but only
the task itself can switch it back to something else. If the task is on
the wake_list, it's state is already RUNNING, but it has not run yet.
That means any other wakeup will jump to the "goto out" and skip over
the ttwu_queue() call.

-- Steve
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