linux-kernel - Re: [PATCH v3 1/4] mtd: rawnand: nand_bbt: hide suspend/resume hooks while scanning bbt

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Date:   Wed, 20 Oct 2021 10:53:26 +0200
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Sean Nyekjaer <sean@...nix.com>
Cc:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <bbrezillon@...nel.org>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/4] mtd: rawnand: nand_bbt: hide suspend/resume
 hooks while scanning bbt

On Wed, 20 Oct 2021 10:45:31 +0200
Sean Nyekjaer <sean@...nix.com> wrote:

> From: Boris Brezillon <boris.brezillon@...labora.com>
> 
> The BBT scan logic use the MTD helpers before the MTD layer had a
> chance to initialize the device, and that leads to issues when
> accessing the uninitialized suspend lock. Let's temporarily set the
> suspend/resume hooks to NULL to skip the lock acquire/release step.
> 
> Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking")
> Tested-by: Sean Nyekjaer <sean@...nix.com>

It's missing our Signed-off-by tags.

> ---
>  drivers/mtd/nand/raw/nand_bbt.c | 28 +++++++++++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/nand/raw/nand_bbt.c b/drivers/mtd/nand/raw/nand_bbt.c
> index b7ad030225f8..93d385703469 100644
> --- a/drivers/mtd/nand/raw/nand_bbt.c
> +++ b/drivers/mtd/nand/raw/nand_bbt.c
> @@ -1397,8 +1397,28 @@ static int nand_create_badblock_pattern(struct nand_chip *this)
>   */
>  int nand_create_bbt(struct nand_chip *this)
>  {
> +	struct mtd_info *mtd = nand_to_mtd(this);
> +	int (*suspend) (struct mtd_info *) = mtd->_suspend;
> +	void (*resume) (struct mtd_info *) = mtd->_resume;
>  	int ret;
>  
> +	/*
> +	 * The BBT scan logic use the MTD helpers before the MTD layer had a
> +	 * chance to initialize the device, and that leads to issues when
> +	 * accessing the uninitialized suspend lock. Let's temporarily set the
> +	 * suspend/resume hooks to NULL to skip the lock acquire/release step.
> +	 *
> +	 * FIXME: This is an ugly hack, so please don't copy this pattern to
> +	 * other MTD implementations. The proper fix would be to implement a
> +	 * generic BBT scan logic at the NAND level that's not using any of the
> +	 * MTD helpers to access pages. We also might consider doing a two
> +	 * step initialization at the MTD level (mtd_device_init() +
> +	 * mtd_device_register()) so some of the fields are initialized
> +	 * early.
> +	 */
> +	mtd->_suspend = NULL;
> +	mtd->_resume = NULL;
> +
>  	/* Is a flash based bad block table requested? */
>  	if (this->bbt_options & NAND_BBT_USE_FLASH) {
>  		/* Use the default pattern descriptors */
> @@ -1422,7 +1442,13 @@ int nand_create_bbt(struct nand_chip *this)
>  			return ret;
>  	}
>  
> -	return nand_scan_bbt(this, this->badblock_pattern);
> +	ret = nand_scan_bbt(this, this->badblock_pattern);
> +
> +	/* Restore the suspend/resume hooks. */
> +	mtd->_suspend = suspend;
> +	mtd->_resume = resume;
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(nand_create_bbt);
>