On Wed, Jul 29, 2015 at 03:38:03AM +0200, Rafael J. Wysocki wrote: > On Monday, July 27, 2015 08:09:35 PM Viresh Kumar wrote: > > On 27-07-15, 15:45, Rafael J. Wysocki wrote: > > > Say the subsys add callback runs for a CPU and it doesn't have a policy. > > > If it is offline, we ignore it and the add callback won't be executed > > > for it again. > > > > > > In turn, if it is online, we create a policy for it and we should (right > > > away) link the policy to all of the CPUs that were offline when the > > > subsys add > > > callback was called for them. That's what we do today. > > > > > > Is there anything missing in that? > > > > So the code is working properly after your patch, but I was talking > > on the lines of what Russell suggested. > > > > We should play with the links only when we receive add-dev/remove-dev > > from subsys callbacks. The exception to that will be the offline CPUs > > for which add-dev is called before their policy existed. > > The rule is supposed to be "all of the present CPUs which do not own > a policy should point to one, unless it doesn't exist". The right > approach is then to create links from them to a policy object as soon > as we create one for them. Waiting for something else to happen is just > pointless and this approach covers both the offline and online CPUs, so > I don't think that changing it would improve things really.
I'm not sure we disagree with that. It's more about when the symlinks are created, and when you define that a CPU exists. If you're attaching to subsystem in sysfs, then the point that the subsystem interface gets to know about a sysfs node existing is when it's add_dev method is called - it should not assume that a node exists prior to that point, otherwise things are racy. Consider a policy initialisation in parallel with an update of the CPU present map and adding a CPU to sysfs. The CPU present map will be updated first, and then it will be added to sysfs. If you're initialising a cpufreq policy in the middle of that and creating symlinks for all present CPUs, there's a window where the CPU present map indicates that a CPU is present, but there is no sysfs directory for you to create a symlink in. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/