[PATCH] powerpc/pseries: Verify CPU doesn't exist before adding

[Denis Kirjanov]

On 10/23/15, Nathan Fontenot <nfont at linux.vnet.ibm.com> wrote:
> When DLPAR adding a CPU we should verify that the CPU does not already
> exist. Failure to do so can generate a kernel oops;
>
> [    9.465585] kernel BUG at arch/powerpc/platforms/pseries/dlpar.c:382!
> [    9.465796] Oops: Exception in kernel mode, sig: 5 [#1]
>
> This oops can be generated by causing a probe to be performed on a cpu
> by writing to the sysfs cpu probe file (/sys/devices/system/cpu/probe).
> This patch adds a check for the existence of cpu prior to probing the cpu
> so userspace doing the wrong thing won't trigger a BUG_ON().

Hi Nathan,

Can you please tell how to trigger the oops manually since I've tried to write
a core number to the probe file, but with no luck. Always get -EINVAL.

Thanks!
>
> Signed-off-by: Nathan Fontenot <nfont at linux.vnet.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/dlpar.c |   43
> +++++++++++++++++++++++++++++---
>  1 file changed, 39 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/platforms/pseries/dlpar.c
> b/arch/powerpc/platforms/pseries/dlpar.c
> index f244dcb..fe6320d 100644
> --- a/arch/powerpc/platforms/pseries/dlpar.c
> +++ b/arch/powerpc/platforms/pseries/dlpar.c
> @@ -381,6 +381,32 @@ out:
>
>  }
>
> +static bool dlpar_cpu_exists(struct device_node *parent, u32 drc_index)
> +{
> +	struct device_node *child = NULL;
> +	u32 my_drc_index;
> +	bool found;
> +	int rc;
> +
> +	/* Assume cpu doesn't exist */
> +	found = false;
> +
> +	for_each_child_of_node(parent, child) {
> +		rc = of_property_read_u32(child, "ibm,my-drc-index",
> +					  &my_drc_index);
> +		if (rc)
> +			continue;
> +
> +		if (my_drc_index == drc_index) {
> +			of_node_put(child);
> +			found = true;
> +			break;
> +		}
> +	}
> +
> +	return found;
> +}
> +
>  static ssize_t dlpar_cpu_probe(const char *buf, size_t count)
>  {
>  	struct device_node *dn, *parent;
> @@ -391,14 +417,23 @@ static ssize_t dlpar_cpu_probe(const char *buf, size_t
> count)
>  	if (rc)
>  		return -EINVAL;
>
> -	rc = dlpar_acquire_drc(drc_index);
> -	if (rc)
> -		return -EINVAL;
> -
>  	parent = of_find_node_by_path("/cpus");
>  	if (!parent)
>  		return -ENODEV;
>
> +	if (dlpar_cpu_exists(parent, drc_index)) {
> +		of_node_put(parent);
> +		printk(KERN_WARNING "CPU with drc index %x already exists\n",
> +		       drc_index);
> +		return -EINVAL;
> +	}
> +
> +	rc = dlpar_acquire_drc(drc_index);
> +	if (rc) {
> +		of_node_put(parent);
> +		return -EINVAL;
> +	}
> +
>  	dn = dlpar_configure_connector(cpu_to_be32(drc_index), parent);
>  	of_node_put(parent);
>  	if (!dn) {
>
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