[PATCH 2/3] powerpc/pseries/mobility: prevent cpu hotplug during DT update

[Gautham R Shenoy]

Hello Nathan,

On Wed, Jun 12, 2019 at 10:19 AM Nathan Lynch <nathanl at linux.ibm.com> wrote:
>
> CPU online/offline code paths are sensitive to parts of the device
> tree (various cpu node properties, cache nodes) that can be changed as
> a result of a migration.
>
> Prevent CPU hotplug while the device tree potentially is inconsistent.
>
> Fixes: 410bccf97881 ("powerpc/pseries: Partition migration in the kernel")
> Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>

Audited the callbacks of of_reconfig_notify(). We are fine with
respect to CPU-Hotplug locking.

Reviewed-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>

> ---
>  arch/powerpc/platforms/pseries/mobility.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/arch/powerpc/platforms/pseries/mobility.c b/arch/powerpc/platforms/pseries/mobility.c
> index 88925f8ca8a0..edc1ec408589 100644
> --- a/arch/powerpc/platforms/pseries/mobility.c
> +++ b/arch/powerpc/platforms/pseries/mobility.c
> @@ -9,6 +9,7 @@
>   * 2 as published by the Free Software Foundation.
>   */
>
> +#include <linux/cpu.h>
>  #include <linux/kernel.h>
>  #include <linux/kobject.h>
>  #include <linux/smp.h>
> @@ -338,11 +339,19 @@ void post_mobility_fixup(void)
>         if (rc)
>                 printk(KERN_ERR "Post-mobility activate-fw failed: %d\n", rc);
>
> +       /*
> +        * We don't want CPUs to go online/offline while the device
> +        * tree is being updated.
> +        */
> +       cpus_read_lock();
> +
>         rc = pseries_devicetree_update(MIGRATION_SCOPE);
>         if (rc)
>                 printk(KERN_ERR "Post-mobility device tree update "
>                         "failed: %d\n", rc);
>
> +       cpus_read_unlock();
> +
>         /* Possibly switch to a new RFI flush type */
>         pseries_setup_rfi_flush();
>
> --
> 2.20.1
>


-- 
Thanks and Regards
gautham.