linux-kernel - Re: [PATCH 3/3] mtd: mtdconcat: add suspend lock handling

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Message-ID: <20211011155805.7793ad21@collabora.com>
Date:   Mon, 11 Oct 2021 15:58:05 +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 3/3] mtd: mtdconcat: add suspend lock handling

On Mon, 11 Oct 2021 13:52:53 +0200
Sean Nyekjaer <sean@...nix.com> wrote:

> Use new suspend lock handling for this special case for concatenated
> MTD devices.
> 
> Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking")
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> ---
>  drivers/mtd/mtdconcat.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
> index f685a581df48..c497c851481f 100644
> --- a/drivers/mtd/mtdconcat.c
> +++ b/drivers/mtd/mtdconcat.c
> @@ -561,25 +561,32 @@ static void concat_sync(struct mtd_info *mtd)
>  
>  static int concat_suspend(struct mtd_info *mtd)
>  {
> +	struct mtd_info *master = mtd_get_master(mtd);
>  	struct mtd_concat *concat = CONCAT(mtd);
>  	int i, rc = 0;
>  
>  	for (i = 0; i < concat->num_subdev; i++) {
>  		struct mtd_info *subdev = concat->subdev[i];
> -		if ((rc = mtd_suspend(subdev)) < 0)
> +
> +		down_write(&master->master.suspend_lock);

You should definitely not take the concat lock here, the framework does
it for you, so all you'll get is a deadlock.

> +		if ((rc = __mtd_suspend(subdev)) < 0)
>  			return rc;

You're returning with the lock held => DEADLOCK next time you try to
acquire it.

Anyway, as mentioned in my review of patch 1, I'd go for this ad-hoc
solution:


	for (i = 0; i < concat->num_subdev; i++) {
		rc = subdev->_suspend ? subdev->_suspend(subdev) : 0;
		if (rc < 0)
			return rc;
	}

	return 0;

> +		up_write(&master->master.suspend_lock);
>  	}
>  	return rc;
>  }
>  
>  static void concat_resume(struct mtd_info *mtd)
>  {
> +	struct mtd_info *master = mtd_get_master(mtd);
>  	struct mtd_concat *concat = CONCAT(mtd);
>  	int i;
>  
>  	for (i = 0; i < concat->num_subdev; i++) {
>  		struct mtd_info *subdev = concat->subdev[i];
> -		mtd_resume(subdev);
> +		down_write(&master->master.suspend_lock);
> +		__mtd_resume(subdev);
> +		up_write(&master->master.suspend_lock);
>  	}

No down/up_write() needed:

  	for (i = 0; i < concat->num_subdev; i++) {
  		struct mtd_info *subdev = concat->subdev[i];
		if (subdev->_resume)
			subdev->_resume(subdev);

	}
>  }
>