On 01/02/2018 09:46 PM, Tejun Heo wrote: > Hello, > > On Fri, Dec 29, 2017 at 02:07:16AM +0530, Prateek Sood wrote: >> task T is waiting for cpuset_mutex acquired >> by kworker/2:1 >> >> sh ==> cpuhp/2 ==> kworker/2:1 ==> sh >> >> kworker/2:3 ==> kthreadd ==> Task T ==> kworker/2:1 >> >> It seems that my earlier patch set should fix this scenario: >> 1) Inverting locking order of cpuset_mutex and cpu_hotplug_lock. >> 2) Make cpuset hotplug work synchronous. >> >> Could you please share your feedback. > > Hmm... this can also be resolved by adding WQ_MEM_RECLAIM to the > synchronize rcu workqueue, right? Given the wide-spread usages of > synchronize_rcu and friends, maybe that's the right solution, or at > least something we also need to do, for this particular deadlock? > > Again, I don't have anything against making the domain rebuliding part > of cpuset operations synchronous and these tricky deadlock scenarios > do indicate that doing so would probably be beneficial. That said, > tho, these scenarios seem more of manifestations of other problems > exposed through kthreadd dependency than anything else. > > Thanks. > Hi TJ, Thanks for suggesting WQ_MEM_RECLAIM solution. My understanding of WQ_MEM_RECLAIM was that it needs to be used for cases where memory pressure could cause deadlocks. In this case it does not seem to be a memory pressure issue. Overloading WQ_MEM_RECLAIM usage for solution to another problem is the correct approach? This scenario can be resolved by using WQ_MEM_RECLAIM and a separate workqueue for rcu. But there seems to be a possibility in future if any cpu hotplug callbacks use other predefined workqueues which do not have WQ_MEM_RECLAIM option. Please let me know your feedback on this. Thanks -- Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc., is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
