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

From: David Laight <david.laight.linux@gmail.com>
To: Arnd Bergmann <arnd@kernel.org>
Cc: Pratyush Yadav <pratyush@kernel.org>,
	Michael Walle <mwalle@kernel.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Richard Weinberger <richard@nod.at>,
	Vignesh Raghavendra <vigneshr@ti.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Takahiro Kuwano <takahiro.kuwano@infineon.com>,
	Tudor Ambarus <tudor.ambarus@linaro.org>,
	HyeongJun An <sammiee5311@gmail.com>,
	linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: spi-nor: reduce stack usage in spi_nor_parse_sfdp()
Date: Wed, 16 Sep 2026 11:05:41 +0100	[thread overview]
Message-ID: <20260916110541.35d70289@pumpkin> (raw)
In-Reply-To: <20260915194203.3511147-1-arnd@kernel.org>

On Tue, 15 Sep 2026 21:40:31 +0200
Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
> 
> Two large spi_nor_flash_parameter structures on a function stack
> is really too much, and this can exceed an otherwise reasonable
> frame limit:
> 
> drivers/mtd/spi-nor/sfdp.c: In function 'spi_nor_parse_sfdp':
> drivers/mtd/spi-nor/sfdp.c:1717:1: error: the frame size of 1600 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
> 
> Change one of them to a dynamic allocation to make this more reasonable.

It wouldn't be much more complicated to do a single kmalloc() for both.
Then replace then memcpy() with structure copies for type safety.

Might stop saskiko bleating as well.

David

> 
> Fixes: d20029474a76 ("mtd: spi-nor: push the rollback mechanism into the sfdp module")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/mtd/spi-nor/sfdp.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/sfdp.c b/drivers/mtd/spi-nor/sfdp.c
> index c21a6953db96..5d0901074f50 100644
> --- a/drivers/mtd/spi-nor/sfdp.c
> +++ b/drivers/mtd/spi-nor/sfdp.c
> @@ -1520,7 +1520,7 @@ 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;
>  	struct sfdp_header header;
>  	struct device *dev = nor->dev;
>  	struct sfdp *sfdp;
> @@ -1532,7 +1532,9 @@ 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. */
>  	err = spi_nor_read_sfdp_dma_unsafe(nor, 0, sizeof(header), &header);
> @@ -1652,6 +1654,8 @@ int spi_nor_parse_sfdp(struct spi_nor *nor)
>  
>  	/* Parse optional parameter tables. */
>  	for (i = 0; i < header.nph; i++) {
> +		struct spi_nor_flash_parameter params2;
> +
>  		memcpy(&params2, nor->params, sizeof(params2));
>  		param_header = &param_headers[i];
>  
> @@ -1711,7 +1715,7 @@ 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;
>  }

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