Messages in this thread | | | Date | Thu, 27 Apr 2017 12:01:57 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [patch V2 00/24] cpu/hotplug: Convert get_online_cpus() to a percpu_rwsem |
| |
On Thu, 27 Apr 2017, Mark Rutland wrote:
> On Thu, Apr 27, 2017 at 10:27:20AM +0200, Sebastian Siewior wrote: > > On 2017-04-26 11:32:36 [+0100], Mark Rutland wrote: > > > > So we could end up calling static_branch_enable_cpuslocked() > > > > without actually holding the lock. Should we do a cpu_hotplug_begin/done in > > > > setup_cpu_feature_capabilities ? I agree it doesn't look that nice. Thoughts ? > > > > > > I agree that's hideous, but it looks like the only choice given the > > > hotplug rwsem cahnges. :/ > > > > would work for you to provide a locked and unlocked version? > > Maybe. Today we have: > > // rwsem unlocked > start_kernel() > ->smp_prepare_boot_cpu() > -->update_cpu_errata_workarounds() > --->update_cpu_capabilities() > > // rwsem locked (by other CPU) > secondary_start_kernel() > ->check_local_cpu_capabilities() > -->update_cpu_errata_workarounds() > --->update_cpu_capabilities() > > With the common chain: > > update_cpu_capabilities() > ->cpus_set_cap() > -->static_branch_enable() > > ... so we could add a update_cpu_capabilities{,_cpuslocked}(), and say > that cpus_set_cap() expects the hotplug rswem to be locked, as per the > below diff.
You just can take the rwsen in smp_prepare_boot_cpu(), so you don't need that conditional thingy at all. Hmm?
Thanks,
tglx
| |