On Tue, 11 Mar 2014 02:03:52 +0530 "Srivatsa S. Bhat" <srivatsa.b...@linux.vnet.ibm.com> wrote:
> Hi, > > Many subsystems and drivers have the need to register CPU hotplug callbacks > from their init routines and also perform initialization for the CPUs that are > already online. But unfortunately there is no race-free way to achieve this > today. > > For example, consider this piece of code: > > get_online_cpus(); > > for_each_online_cpu(cpu) > init_cpu(cpu); > > register_cpu_notifier(&foobar_cpu_notifier); > > put_online_cpus(); > > This is not safe because there is a possibility of an ABBA deadlock involving > the cpu_add_remove_lock and the cpu_hotplug.lock. > > CPU 0 CPU 1 > ----- ----- > > Acquire cpu_hotplug.lock > [via get_online_cpus()] > > CPU online/offline operation > takes cpu_add_remove_lock > [via cpu_maps_update_begin()] > > Try to acquire > cpu_add_remove_lock > [via register_cpu_notifier()] > > CPU online/offline operation > tries to acquire > cpu_hotplug.lock > [via cpu_hotplug_begin()] Can't we fix this by using a different (ie: new) lock to protect cpu_chain? _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
