Messages in this thread | | | From | Rusty Russell <> | Subject | Re: keventd_create_kthread | Date | Thu, 19 Feb 2004 20:46:58 +1100 |
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In message <Pine.LNX.4.58.0402190205040.16515@devserv.devel.redhat.com> you write: > The current wait_task_inactive() code seems to be OK on x86. > Context-switching cannot be preempted. The goal of wait_task_inactive() is > to wait for the task to unschedule on a CPU. If that's due to preempt then > it's due to preempt.
No, because it can come back at any time 8(
> that in any modern interface. Why does keventd_create_kthread() need > wait_task_inactive()?
Um, the code was taken from sched.c to kthread:
2.6.3 migration_thread(): set_current_state(TASK_UNINTERRUPTIBLE); schedule();
2.6.3 migration_call(): kernel_thread(migration_thread, &startup, CLONE_KERNEL); wait_for_completion(&startup.startup_done); wait_task_inactive(startup.task);
startup.task->thread_info->cpu = cpu; startup.task->cpus_allowed = cpumask_of_cpu(cpu);
So, if the migration thread has been preempted immediately before schedule(), wait_task_inactive returns, but it can come back from preempt while we're messing with startup.task->thread_info->cpu.
Now, the latter part is wrapped in kthread_bind(), which should really be doing the wait_task_inactive itself (doing it in kthread_create is overzealous). But the race is still there.
Hope that clarifies, Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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