Messages in this thread | | | Date | Thu, 7 Dec 2006 11:47:01 +0530 | From | Srivatsa Vaddagiri <> | Subject | Re: workqueue deadlock |
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On Wed, Dec 06, 2006 at 05:26:14PM -0700, Bjorn Helgaas wrote: > loadkeys is holding the cpu_hotplug lock (acquired in flush_workqueue()) > and waiting in flush_cpu_workqueue() until the cpu_workqueue drains. > > But events/4 is responsible for draining it, and it is blocked waiting > to acquire the cpu_hotplug lock. > > In current upstream, the cpu_hotplug lock has been replaced with > workqueue_mutex, but it looks to me like the same deadlock is still > possible.
Yes I think so too.
> Is there some rule that workqueue functions shouldn't try to > flush a workqueue?
In general, workqueue functions wanting to flush workqueue seems wierd to me. But in this case, I think the requirement is to block until all queued work is complete, which is what flush_workqueue is supposed to do. Hence I dont see any way to avoid it ..
> Or should flush_workqueue() be smarter by > releasing the workqueue_mutex once in a while?
IMHO, rehauling lock_cpu_hotplug() to support scenarios like this is a better approach.
- Make it rw-sem - Make it per-cpu mutex, which could be either:
http://lkml.org/lkml/2006/11/30/110 - Ingo's suggestion http://lkml.org/lkml/2006/10/26/65 - Gautham's work based on RCU
In Ingo's suggestion, I really dont know if the task_struct modifications is a good thing (to support recursive requirements). Gautham's patches avoid modifications to task_struct, is fast but can starve writers (who want to bring down/up a CPU).
-- Regards, vatsa - 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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