Messages in this thread | | | Date | Fri, 16 May 2014 08:16:31 -0400 | From | Tejun Heo <> | Subject | Re: workqueue: WARN at at kernel/workqueue.c:2176 |
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On Fri, May 16, 2014 at 02:14:05PM +0200, Thomas Gleixner wrote: > On Fri, 16 May 2014, Tejun Heo wrote: > > On Fri, May 16, 2014 at 01:57:37PM +0200, Peter Zijlstra wrote: > > > This of course leaves the question how the workqueue code manages to > > > call set_cpu_allowed_ptr() on a cpu _before_ its online. > > > > > > That too sounds fishy.. with the proposed patch the > > > set_cpus_allowed_ptr() will 'gracefully' fail, but calling it in the > > > first place is of course dubious too. > > > > Right after being created, a workqueue worker invokes > > set_cpus_allowed_ptr() to the target cpumask without checking whether > > the cpu[s] are online or not and it's allowed to fail. The guarantee > > there is that the worker is already registered by that point and if a > > CPU comes online after the registration, CPU_ONLINE notification will > > update the cpumask accordingly, so either way the worker is guaranteed > > to be on the right cpumask. > > That's what the kthread_create_on_cpu/kthread_park/kthread_unpark > infrastructure is for.
They aren't necessarily on one CPU. Unbound workqueues can have arbitrary cpumasks associated with them.
Thanks.
-- tejun
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