Messages in this thread |  | | Date | Fri, 25 Aug 2017 18:21:05 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: WARNING: possible circular locking dependency detected |
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On Sat, 26 Aug 2017, Byungchul Park wrote: > On Fri, Aug 25, 2017 at 11:47 PM, Sebastian Andrzej Siewior > <bigeasy@linutronix.de> wrote: > > We hold the sparse_irq_lock lock while waiting for the completion in the > > CPU-down case and in the CPU-up case we acquire the sparse_irq_lock lock > > while the other CPU is waiting for the completion. > > This is not an issue if my interpretation of lockdep here is correct. > > Hello Sebastian, > > I think you parsed the message correctly. > > The message is saying that, for example: > > context A (maybe being up?) > -- > lock(sparse_irq_lock) // wait for sparse_irq_lock in B to be released > complete(st->done) // impossible to hit here > > context B (maybe wanting to synchronize with the cpu being up?) > -- > lock(sparse_irq_lock) // acquired successfully > wait_for_completion(st->done) // wait for completion of st->done in A > unlock(sparse_irq_lock) // impossible to hit here > > I cannot check the kernel code at the moment.. I wonder if this scenario is > impossible. Could you answer it?
Yes, it's impossible because cpu hotplug is globally serialized. So the cpu down scenario cannot happen in parallel with the cpu up scenario.
Thanks,
tglx
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