linux-kernel - Re: [PATCH 4/9] bdi: add a ->dev_name field to struct backing_dev

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Message-ID: <20200422090832.GE8775@quack2.suse.cz>
Date:   Wed, 22 Apr 2020 11:08:32 +0200
From:   Jan Kara <jack@...e.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, yuyufen@...wei.com, tj@...nel.org, jack@...e.cz,
        bvanassche@....org, tytso@....edu, hdegoede@...hat.com,
        gregkh@...uxfoundation.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/9] bdi: add a ->dev_name field to struct
 backing_dev_info

On Wed 22-04-20 09:38:46, Christoph Hellwig wrote:
> Cache a copy of the name for the life time of the backing_dev_info
> structure so that we can reference it even after unregistering.
> 
> Fixes: 68f23b89067f ("memcg: fix a crash in wb_workfn when a device disappears")
> Reported-by: Yufen Yu <yuyufen@...wei.com>
> Signed-off-by: Christoph Hellwig <hch@....de>

Looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  include/linux/backing-dev-defs.h | 1 +
>  mm/backing-dev.c                 | 5 +++--
>  2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
> index 4fc87dee005a..2849bdbb3acb 100644
> --- a/include/linux/backing-dev-defs.h
> +++ b/include/linux/backing-dev-defs.h
> @@ -220,6 +220,7 @@ struct backing_dev_info {
>  	wait_queue_head_t wb_waitq;
>  
>  	struct device *dev;
> +	char dev_name[64];
>  	struct device *owner;
>  
>  	struct timer_list laptop_mode_wb_timer;
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index c2c44c89ee5d..efc5b83acd2d 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -938,7 +938,8 @@ int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
>  	if (bdi->dev)	/* The driver needs to use separate queues per device */
>  		return 0;
>  
> -	dev = device_create_vargs(bdi_class, NULL, MKDEV(0, 0), bdi, fmt, args);
> +	vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);
> +	dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);
>  	if (IS_ERR(dev))
>  		return PTR_ERR(dev);
>  
> @@ -1047,7 +1048,7 @@ const char *bdi_dev_name(struct backing_dev_info *bdi)
>  {
>  	if (!bdi || !bdi->dev)
>  		return bdi_unknown_name;
> -	return dev_name(bdi->dev);
> +	return bdi->dev_name;
>  }
>  EXPORT_SYMBOL_GPL(bdi_dev_name);
>  
> -- 
> 2.26.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR