Re: [PATCH v2] cxl/acpi: Cleanup __cxl_parse_cfmws()

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Wed, 2024-02-28 at 12:30 -0800, Dan Williams wrote:
> As a follow on to the recent rework of __cxl_parse_cfmws() to always
> return errors [1], use cleanup.h helpers to remove goto and other cleanups
> now that logging is moved to the cxl_parse_cfmws() wrapper.
> 
> This ends up adding more code than it deletes, but __cxl_parse_cfmws()
> itself does get smaller. The takeaway from the cond_no_free_ptr()
> discussion [2] was to not add new macros to handle the cases where
> no_free_ptr() is awkward, instead rework the code to have helpers and
> clearer delineation of responsibility.
> 
> Now one might say that  __free(del_cxl_resource) is excessive given it
> is immediately registered with add_or_reset_cxl_resource(). The
> rationale for keeping it is that it forces use of "no_free_ptr()" on the
> argument passed to add_or_reset_cxl_resource(). That in turn makes it
> clear that @res is NULL for the rest of the function which is part of
> the point of the cleanup helpers, to turn subtle use after free errors
> [3] into loud NULL pointer de-references.
> 
> Link: http://lore.kernel.org/r/170820177238.631006.1012639681618409284.stgit@dwillia2-xfh.jf.intel.com [1]
> Link: http://lore.kernel.org/r/CAHk-=whBVhnh=KSeBBRet=E7qJAwnPR_aj5em187Q3FiD+LXnA@mail.gmail.com [2]
> Link: http://lore.kernel.org/r/20230714093146.2253438-1-leitao@debian.org [3]
> Reported-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> Closes: http://lore.kernel.org/r/20240219124041.00002bda@Huawei.com
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

The helpers make sense, and overall looks good to me.

Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>

> ---
> Changes since v1:
> - drop the introduction of cond_no_free_ptr() in favor of reorganizing
>   the code to clarify the handoff of "free on error" responsibility.
> 
>  drivers/cxl/acpi.c |   99 ++++++++++++++++++++++++++++++----------------------
>  drivers/cxl/cxl.h  |    5 +++
>  2 files changed, 62 insertions(+), 42 deletions(-)
> 
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index 1a3e6aafbdcc..1a47207932e2 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -316,28 +316,64 @@ static const struct cxl_root_ops acpi_root_ops = {
>  	.qos_class = cxl_acpi_qos_class,
>  };
>  
> +static void del_cxl_resource(struct resource *res)
> +{
> +	if (!res)
> +		return;
> +	kfree(res->name);
> +	kfree(res);
> +}
> +
> +static struct resource *alloc_cxl_resource(resource_size_t base,
> +					   resource_size_t n, const char *fmt,
> +					   ...)
> +{
> +	va_list ap;
> +
> +	struct resource *res __free(kfree) = kzalloc(sizeof(*res), GFP_KERNEL);
> +	if (!res)
> +		return NULL;
> +
> +	res->start = base;
> +	res->end = base + n - 1;
> +	res->flags = IORESOURCE_MEM;
> +
> +	va_start(ap, fmt);
> +	res->name = kvasprintf(GFP_KERNEL, fmt, ap);
> +	va_end(ap);
> +
> +	if (!res->name)
> +		return NULL;
> +	return no_free_ptr(res);
> +}
> +
> +static int add_or_reset_cxl_resource(struct resource *parent, struct resource *res)
> +{
> +	int rc = insert_resource(parent, res);
> +
> +	if (rc)
> +		del_cxl_resource(res);
> +	return rc;
> +}
> +
> +DEFINE_FREE(put_cxlrd, struct cxl_root_decoder *,
> +	    if (!IS_ERR_OR_NULL(_T)) put_device(&_T->cxlsd.cxld.dev))
> +DEFINE_FREE(del_cxl_resource, struct resource *, if (_T) del_cxl_resource(_T))
>  static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>  			     struct cxl_cfmws_context *ctx)
>  {
>  	int target_map[CXL_DECODER_MAX_INTERLEAVE];
>  	struct cxl_port *root_port = ctx->root_port;
> -	struct resource *cxl_res = ctx->cxl_res;
>  	struct cxl_cxims_context cxims_ctx;
> -	struct cxl_root_decoder *cxlrd;
>  	struct device *dev = ctx->dev;
>  	cxl_calc_hb_fn cxl_calc_hb;
>  	struct cxl_decoder *cxld;
>  	unsigned int ways, i, ig;
> -	struct resource *res;
>  	int rc;
>  
>  	rc = cxl_acpi_cfmws_verify(dev, cfmws);
> -	if (rc) {
> -		dev_err(dev, "CFMWS range %#llx-%#llx not registered\n",
> -			cfmws->base_hpa,
> -			cfmws->base_hpa + cfmws->window_size - 1);
> +	if (rc)
>  		return rc;
> -	}
>  
>  	rc = eiw_to_ways(cfmws->interleave_ways, &ways);
>  	if (rc)
> @@ -348,29 +384,24 @@ static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>  	for (i = 0; i < ways; i++)
>  		target_map[i] = cfmws->interleave_targets[i];
>  
> -	res = kzalloc(sizeof(*res), GFP_KERNEL);
> +	struct resource *res __free(del_cxl_resource) =
> +		alloc_cxl_resource(cfmws->base_hpa, cfmws->window_size,
> +				   "CXL Window %d", ctx->id++);
>  	if (!res)
>  		return -ENOMEM;
>  
> -	res->name = kasprintf(GFP_KERNEL, "CXL Window %d", ctx->id++);
> -	if (!res->name)
> -		goto err_name;
> -
> -	res->start = cfmws->base_hpa;
> -	res->end = cfmws->base_hpa + cfmws->window_size - 1;
> -	res->flags = IORESOURCE_MEM;
> -
>  	/* add to the local resource tracking to establish a sort order */
> -	rc = insert_resource(cxl_res, res);
> +	rc = add_or_reset_cxl_resource(ctx->cxl_res, no_free_ptr(res));
>  	if (rc)
> -		goto err_insert;
> +		return rc;
>  
>  	if (cfmws->interleave_arithmetic == ACPI_CEDT_CFMWS_ARITHMETIC_MODULO)
>  		cxl_calc_hb = cxl_hb_modulo;
>  	else
>  		cxl_calc_hb = cxl_hb_xor;
>  
> -	cxlrd = cxl_root_decoder_alloc(root_port, ways, cxl_calc_hb);
> +	struct cxl_root_decoder *cxlrd __free(put_cxlrd) =
> +		cxl_root_decoder_alloc(root_port, ways, cxl_calc_hb);
>  	if (IS_ERR(cxlrd))
>  		return PTR_ERR(cxlrd);
>  
> @@ -378,8 +409,8 @@ static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>  	cxld->flags = cfmws_to_decoder_flags(cfmws->restrictions);
>  	cxld->target_type = CXL_DECODER_HOSTONLYMEM;
>  	cxld->hpa_range = (struct range) {
> -		.start = res->start,
> -		.end = res->end,
> +		.start = cfmws->base_hpa,
> +		.end = cfmws->base_hpa + cfmws->window_size - 1,
>  	};
>  	cxld->interleave_ways = ways;
>  	/*
> @@ -399,11 +430,10 @@ static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>  			rc = acpi_table_parse_cedt(ACPI_CEDT_TYPE_CXIMS,
>  						   cxl_parse_cxims, &cxims_ctx);
>  			if (rc < 0)
> -				goto err_xormap;
> +				return rc;
>  			if (!cxlrd->platform_data) {
>  				dev_err(dev, "No CXIMS for HBIG %u\n", ig);
> -				rc = -EINVAL;
> -				goto err_xormap;
> +				return -EINVAL;
>  			}
>  		}
>  	}
> @@ -411,18 +441,9 @@ static int __cxl_parse_cfmws(struct acpi_cedt_cfmws *cfmws,
>  	cxlrd->qos_class = cfmws->qtg_id;
>  
>  	rc = cxl_decoder_add(cxld, target_map);
> -err_xormap:
>  	if (rc)
> -		put_device(&cxld->dev);
> -	else
> -		rc = cxl_decoder_autoremove(dev, cxld);
> -	return rc;
> -
> -err_insert:
> -	kfree(res->name);
> -err_name:
> -	kfree(res);
> -	return -ENOMEM;
> +		return rc;
> +	return cxl_root_decoder_autoremove(dev, no_free_ptr(cxlrd));
>  }
>  
>  static int cxl_parse_cfmws(union acpi_subtable_headers *header, void *arg,
> @@ -692,12 +713,6 @@ static void cxl_acpi_lock_reset_class(void *dev)
>  	device_lock_reset_class(dev);
>  }
>  
> -static void del_cxl_resource(struct resource *res)
> -{
> -	kfree(res->name);
> -	kfree(res);
> -}
> -
>  static void cxl_set_public_resource(struct resource *priv, struct resource *pub)
>  {
>  	priv->desc = (unsigned long) pub;
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 003feebab79b..8bc044a4a965 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -776,6 +776,11 @@ int cxl_decoder_add(struct cxl_decoder *cxld, int *target_map);
>  struct cxl_endpoint_decoder *cxl_endpoint_decoder_alloc(struct cxl_port *port);
>  int cxl_decoder_add_locked(struct cxl_decoder *cxld, int *target_map);
>  int cxl_decoder_autoremove(struct device *host, struct cxl_decoder *cxld);
> +static inline int cxl_root_decoder_autoremove(struct device *host,
> +					      struct cxl_root_decoder *cxlrd)
> +{
> +	return cxl_decoder_autoremove(host, &cxlrd->cxlsd.cxld);
> +}
>  int cxl_endpoint_autoremove(struct cxl_memdev *cxlmd, struct cxl_port *endpoint);
>  
>  /**
> 
>