Re: [PATCH] sched: CPU hotplug race vs. set_cpus_allowed()

[Con Kolivas <kernel@kolivas.org>]

On Friday 23 June 2006 18:16, Kirill Korotaev wrote:
> Looks like there is a race between set_cpus_allowed()
> and move_task_off_dead_cpu().
> __migrate_task() doesn't report any err code, so
> task can be left on its runqueue if its cpus_allowed mask
> changed so that dest_cpu is not longer a possible target.
> Also, chaning cpus_allowed mask requires rq->lock being held.
>
> Signed-Off-By: Kirill Korotaev <dev@openvz.org>
>
> Kirill
> P.S. against 2.6.17-mm1

Hi!

Since you've got

-static void __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
+static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
 {
        runqueue_t *rq_dest, *rq_src;
+       int res = 0;
 
        if (unlikely(cpu_is_offline(dest_cpu)))
-               return;
+               return 0;

why not return res here?

oh and ret is a more commonly used name than res (your choice of course).

and an addition to the comment such as "returns non-zero only when it fails to 
migrate the task" would be nice.

thanks!

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