Re: [PATCH] mtd: spi-nor: reduce stack usage in spi_nor_parse_sfdp()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] mtd: spi-nor: mixing goto and scope-based cleanup in spi_nor_parse_sfdp()
- [Low] mtd: spi-nor: split definition and initialization of __free() variable
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commit 1f040dc109ef8aa4b9fc1c81bcaa8f6e6a5a27c0
Author: Arnd Bergmann <arnd@arndb.de>

mtd: spi-nor: reduce stack usage in spi_nor_parse_sfdp()

This commit reduces stack usage in spi_nor_parse_sfdp() by replacing an
on-stack struct spi_nor_flash_parameter variable with a dynamically allocated
one. It utilizes the __free(kfree) scope-based cleanup helper to manage the
allocated memory.

> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
> index 641f17ad51a09..466558ea528d8 100644
> --- a/drivers/mtd/spi-nor/sfdp.c
> +++ b/drivers/mtd/spi-nor/sfdp.c
> @@ -1521,7 +1521,7 @@ int spi_nor_parse_sfdp(struct spi_nor *nor)
>  {
>  	const struct sfdp_parameter_header *param_header, *bfpt_header;
>  	struct sfdp_parameter_header *param_headers = NULL;
> -	struct spi_nor_flash_parameter params, params2;
> +	struct spi_nor_flash_parameter __free(kfree) *params = NULL;

[Severity: Low]
Does this split definition and initialization of the params pointer violate
the cleanup subsystem guidelines?

The guidelines recommend defining and initializing scope-based cleanup
variables in a single statement (such as at the kmemdup call below) rather
than initializing to NULL at the top with assignment later. While this
specific case might not trigger a LIFO ordering bug since there are no
guard() locks present, it does bypass the subsystem recommendation designed
to prevent those ordering mistakes.

>  	struct sfdp_header header;
>  	struct device *dev = nor->dev;
>  	struct sfdp *sfdp;
> @@ -1533,7 +1533,9 @@ int spi_nor_parse_sfdp(struct spi_nor *nor)
>  	 * Get a backup of all the parameter to roll back to in case of an
>  	 * error.
>  	 */
> -	memcpy(&params, nor->params, sizeof(params));
> +	params = kmemdup(nor->params, sizeof(*params), GFP_KERNEL);
> +	if (!params)
> +		return -ENOMEM;
>  
>  	/* Get the SFDP header. */

[ ... ]

> @@ -1712,7 +1716,7 @@ int spi_nor_parse_sfdp(struct spi_nor *nor)
>  free_param_headers:
>  	kfree(param_headers);
>  	if (err)
> -		memcpy(nor->params, &params, sizeof(*nor->params));
> +		memcpy(nor->params, params, sizeof(*nor->params));
>  
>  	return err;
>  }

[Severity: Medium]
Is it safe to mix goto-based error handling with scope-based cleanup in
this function?

The kernel cleanup subsystem guidelines dictate that goto-based error
handling and scope-based cleanups should never be mixed in the same
function. Retaining the free_param_headers goto label and other manual
cleanups in spi_nor_parse_sfdp() while introducing __free(kfree) for params
violates the 'all-or-nothing' conversion rule and can create confusing
ownership semantics.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260915194203.3511147-1-arnd@kernel.org?part=1