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Date: Thu, 30 Aug 2012 17:16:01 +0800 From: Lai Jiangshan <laijs@...fujitsu.com> To: Tejun Heo <tj@...nel.org> CC: linux-kernel@...r.kernel.org Subject: Re: [PATCH 4/9 V3] workqueue: add non_manager_role_manager_mutex_unlock() On 08/30/2012 02:25 AM, Tejun Heo wrote: > On Thu, Aug 30, 2012 at 12:51:55AM +0800, Lai Jiangshan wrote: >> If hotplug code grabbed the manager_mutex and worker_thread try to create >> a worker, the manage_worker() will return false and worker_thread go to >> process work items. Now, on the CPU, all workers are processing work items, >> no idle_worker left/ready for managing. It breaks the concept of workqueue >> and it is bug. >> >> So when this case happens, the last idle should not go to process work, >> it should go to sleep as usual and wait normal events. but it should >> also be notified by the event that hotplug code release the manager_mutex. >> >> So we add non_manager_role_manager_mutex_unlock() to do this notify. > > Hmmm... how about just running rebind_workers() from a work item? > That way, it would be guaranteed that there alwyas will be an extra > worker available on rebind completion. > > Thanks. > gcwq_unbind_fn() is unsafe even it is called from a work item. so we need non_manager_role_manager_mutex_unlock(). If rebind_workers() is called from a work item, it is safe when there is no CPU_INTENSIVE items. but we can't disable CPU_INTENSIVE items, so it is still unsafe, we need non_manager_role_manager_mutex_unlock() too. non_manager_role_manager_mutex_unlock() approach is good to fix it. I'm writing V4 patch/approach to fix it too, it is a little more complicated, but it has some benefit over non_manager_role_manager_mutex_unlock() approach. Thanks. Lai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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