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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
