Messages in this thread | | | Date | Tue, 12 Jul 2022 06:13:46 -1000 | From | Tejun Heo <> | Subject | Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu hotplug when using schedutil |
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On Tue, Jul 12, 2022 at 01:57:02PM +0100, Qais Yousef wrote: > Is there a lot of subsystems beside cpuset that needs the cpus_read_lock()? > A quick grep tells me it's the only one. > > Can't we instead use cpus_read_trylock() in cpuset_can_attach() so that we > either hold the lock successfully then before we go ahead and call > cpuset_attach(), or bail out and cancel the whole attach operation which should > unlock the threadgroup_rwsem() lock?
But now we're failing user-initiated operations randomly. I have a hard time seeing that as an acceptable solution. The only thing we can do, I think, is establishing a locking order between the two locks by either nesting threadgroup_rwsem under cpus_read_lock or disallowing thread creation during hotplug operations.
Thanks.
-- tejun
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