Messages in this thread Patch in this message | | | Subject | [patch, rfc: 2/2] sched, hotplug: ensure a task is on the valid cpu after set_cpus_allowed_ptr() | From | Dmitry Adamushko <> | Date | Fri, 25 Jul 2008 00:15:30 +0200 |
| |
From: Dmitry Adamushko <dmitry.adamushko@gmail.com> Subject: sched, hotplug: ensure a task is on the valid cpu after set_cpus_allowed_ptr()
--- sched, hotplug: ensure a task is on the valid cpu after set_cpus_allowed_ptr() The 'new_mask' may not include task_cpu(p) so we migrate 'p' on another 'cpu'. In case it can't be placed on this 'cpu' immediately, we submit a request to the migration thread and wait for its completion. Now, by the moment this request gets handled by the migration_thread, 'cpu' may well be offline/non-active. As a result, 'p' continues running on its old cpu which is not in the 'new_mask'. Fix it: ensure 'p' ends up on a valid cpu. Theoreticaly (but unlikely), we may get an endless loop if someone cpu_down()'s a new cpu we have choosen on each iteration. Alternatively, we may introduce a special type of request to migration_thread, namely "move_to_any_allowed_cpu" (e.g. by specifying dest_cpu == -1). Note, any_active_cpu() instead of any_online_cpu() would be better here. Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
diff --git a/kernel/sched.c b/kernel/sched.c index b4ccc8b..c3bd78a 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5774,21 +5774,23 @@ int set_cpus_allowed_ptr(struct task_struct *p, const cpumask_t *new_mask) } /* Can the task run on the task's current CPU? If so, we're done */ - if (cpu_isset(task_cpu(p), *new_mask)) - goto out; + while (!cpu_isset(task_cpu(p), p->cpus_allowed)) { + int cpu = any_online_cpu(p->cpus_allowed); - if (migrate_task(p, any_online_cpu(*new_mask), &req)) { - /* Need to wait for migration thread (might exit: take ref). */ - struct task_struct *mt = rq->migration_thread; + if (migrate_task(p, cpu, &req)) { + /* Need to wait for migration thread (might exit: take ref). */ + struct task_struct *mt = rq->migration_thread; - get_task_struct(mt); - task_rq_unlock(rq, &flags); - wake_up_process(mt); - put_task_struct(mt); + get_task_struct(mt); + task_rq_unlock(rq, &flags); + wake_up_process(mt); + put_task_struct(mt); - wait_for_completion(&req.done); - tlb_migrate_finish(p->mm); - return 0; + wait_for_completion(&req.done); + tlb_migrate_finish(p->mm); + + rq = task_rq_lock(p, &flags); + } } out: task_rq_unlock(rq, &flags);
| |