linux-kernel - Re: [PATCH v3 2/4] mtd: mtdconcat: add suspend lock handling

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Message-ID: <20211025165957.349a6580@collabora.com>
Date:   Mon, 25 Oct 2021 16:59:57 +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 2/4] mtd: mtdconcat: add suspend lock handling

Hello Sean,

On Mon, 25 Oct 2021 11:27:50 +0200
Sean Nyekjaer <sean@...nix.com> wrote:

The subject is misleading, how about 'mtd: mtdconcat: Don't use
mtd_{suspend,resume}()'

> Use MTD hooks to control suspend/resume of MTD devices.
> concat_{suspend,resume} will be called from mtd_{suspend,resume},
> which already have taken the suspend/resume lock.
> It's safe to proceed with calling MTD device hooks directly from here.

"
The MTD suspend logic will soon be adjusted to automatically wait for
device wake-up before issuing IOs. In order to do that a new read-write
lock will be added and taken in write-mode in the
mtd_{suspend,resume}() path. Since mtdconcat.c itself is an MTD device,
calling mtd_suspend/resume() on subdevices from the mtdconcat
->_{suspend,resume}() hook will lead to a nested lock, which lockdep
will complain about if we don't add a proper annotation. Let's keep
things simple and replace those mtd_{suspend,resume}(subdev) calls by
subdev->_{suspend,resume}() ones to avoid this situation.
"

> 
> Fixes: 013e6292aaf5 ("mtd: rawnand: Simplify the locking")

Again, this commit doesn't fix anything.

> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Sean Nyekjaer <sean@...nix.com>
> ---
>  drivers/mtd/mtdconcat.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/mtdconcat.c b/drivers/mtd/mtdconcat.c
> index f685a581df48..37532f529820 100644
> --- a/drivers/mtd/mtdconcat.c
> +++ b/drivers/mtd/mtdconcat.c
> @@ -566,9 +566,15 @@ static int concat_suspend(struct mtd_info *mtd)
>  
>  	for (i = 0; i < concat->num_subdev; i++) {
>  		struct mtd_info *subdev = concat->subdev[i];
> -		if ((rc = mtd_suspend(subdev)) < 0)
> +		/*
> +		 * Call MTD hook directly from here,
> +		 * mtd_suspend() have the suspend/resume lock.

		/*
		 * Call the MTD hook directly to avoid a nested lock
		 * on ->suspend_lock.
		 */

> +		 */
> +		rc = subdev->_suspend ? subdev->_suspend(subdev) : 0;
> +		if (rc < 0)
>  			return rc;
>  	}
> +
>  	return rc;
>  }
>  
> @@ -579,7 +585,12 @@ static void concat_resume(struct mtd_info *mtd)
>  
>  	for (i = 0; i < concat->num_subdev; i++) {
>  		struct mtd_info *subdev = concat->subdev[i];
> -		mtd_resume(subdev);
> +		/*
> +		 * Call MTD hook directly from here,
> +		 * mtd_resume() have the suspend/resume lock.
> +		 */

Ditto.

> +		if (subdev->_resume)
> +			subdev->_resume(subdev);
>  	}
>  }
>