Re: [PATCH v10 4/6] powerpc/papr_scm: Improve error logging and handling papr_scm_ndctl()

[Ira Weiny]

On Fri, Jun 05, 2020 at 05:11:34AM +0530, Vaibhav Jain wrote:
> Since papr_scm_ndctl() can be called from outside papr_scm, its
> exposed to the possibility of receiving NULL as value of 'cmd_rc'
> argument. This patch updates papr_scm_ndctl() to protect against such
> possibility by assigning it pointer to a local variable in case cmd_rc
> == NULL.
> 
> Finally the patch also updates the 'default' clause of the switch-case
> block removing a 'return' statement thereby ensuring that value of
> 'cmd_rc' is always logged when papr_scm_ndctl() returns.
> 
> Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>
> ---
> Changelog:
> 
> v9..v10
> * New patch in the series

Thanks for making this a separate patch it is easier to see what is going on
here.

> ---
>  arch/powerpc/platforms/pseries/papr_scm.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 0c091622b15e..6512fe6a2874 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -355,11 +355,16 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>  {
>  	struct nd_cmd_get_config_size *get_size_hdr;
>  	struct papr_scm_priv *p;
> +	int rc;
>  
>  	/* Only dimm-specific calls are supported atm */
>  	if (!nvdimm)
>  		return -EINVAL;
>  
> +	/* Use a local variable in case cmd_rc pointer is NULL */
> +	if (!cmd_rc)
> +		cmd_rc = &rc;
> +

This protects you from the NULL.  However...

>  	p = nvdimm_provider_data(nvdimm);
>  
>  	switch (cmd) {
> @@ -381,12 +386,13 @@ static int papr_scm_ndctl(struct nvdimm_bus_descriptor *nd_desc,
>  		break;
>  
>  	default:
> -		return -EINVAL;
> +		dev_dbg(&p->pdev->dev, "Unknown command = %d\n", cmd);
> +		*cmd_rc = -EINVAL;

... I think you are conflating rc and cmd_rc...

>  	}
>  
>  	dev_dbg(&p->pdev->dev, "returned with cmd_rc = %d\n", *cmd_rc);
>  
> -	return 0;
> +	return *cmd_rc;

... this changes the behavior of the current commands.  Now if the underlying
papr_scm_meta_[get|set]() fails you return that failure as rc rather than 0.

Is that ok?

Also 'logging cmd_rc' in the invalid cmd case does not seem quite right unless
you really want rc to be cmd_rc.

The architecture is designed to separate errors which occur in the kernel vs
errors in the firmware/dimm.  Are they always the same?  The current code
differentiates them.

Ira

>  }
>  
>  static ssize_t flags_show(struct device *dev,
> -- 
> 2.26.2
>