On Thursday 06 February 2014 03:36 AM, Srivatsa S. Bhat wrote:
> Subsystems that want to register CPU hotplug callbacks, as well as perform
> initialization for the CPUs that are already online, often do it as shown
> below:
>
> get_online_cpus();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> register_cpu_notifier(&foobar_cpu_notifier);
>
> put_online_cpus();
>
> This is wrong, since it is prone to ABBA deadlocks involving the
> cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
> with CPU hotplug operations).
>
> Instead, the correct and race-free way of performing the callback
> registration is:
>
> cpu_maps_update_begin();
>
> for_each_online_cpu(cpu)
> init_cpu(cpu);
>
> /* Note the use of the double underscored version of the API */
> __register_cpu_notifier(&foobar_cpu_notifier);
>
> cpu_maps_update_done();
>
>
> Fix the sysfs code in powerpc by using this latter form of callback
> registration.
Acked-by: Madhavan Srinivasan <ma...@linux.vnet.ibm.com>
>
> Cc: Benjamin Herrenschmidt <b...@kernel.crashing.org>
> Cc: Paul Mackerras <pau...@samba.org>
> Cc: Madhavan Srinivasan <ma...@linux.vnet.ibm.com>
> Cc: Olof Johansson <o...@lixom.net>
> Cc: Wang Dongsheng <dongsheng.w...@freescale.com>
> Cc: linuxppc-...@lists.ozlabs.org
> Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
> ---
>
> arch/powerpc/kernel/sysfs.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
> index 97e1dc9..c29ad44 100644
> --- a/arch/powerpc/kernel/sysfs.c
> +++ b/arch/powerpc/kernel/sysfs.c
> @@ -975,7 +975,8 @@ static int __init topology_init(void)
> int cpu;
>
> register_nodes();
> - register_cpu_notifier(&sysfs_cpu_nb);
> +
> + cpu_maps_update_begin();
>
> for_each_possible_cpu(cpu) {
> struct cpu *c = &per_cpu(cpu_devices, cpu);
> @@ -999,6 +1000,11 @@ static int __init topology_init(void)
> if (cpu_online(cpu))
> register_cpu_online(cpu);
> }
> +
> + __register_cpu_notifier(&sysfs_cpu_nb);
> +
> + cpu_maps_update_done();
> +
> #ifdef CONFIG_PPC64
> sysfs_create_dscr_default();
> #endif /* CONFIG_PPC64 */
>
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