linux-kernel - Re: [PATCH] bcache: move calc_cached_dev_sectors to proper place on backing device detach

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Message-ID: <fcae5dd6-ddd7-d402-fed2-a42a473cf823@suse.de>
Date:   Mon, 18 Oct 2021 22:38:37 +0800
From:   Coly Li <colyli@...e.de>
To:     Lin Feng <linf@...gsu.com>
Cc:     linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org,
        kent.overstreet@...il.com
Subject: Re: [PATCH] bcache: move calc_cached_dev_sectors to proper place on
 backing device detach

On 10/15/21 6:16 PM, Lin Feng wrote:
> Calculation of cache_set's cached sectors is done by travelling
> cached_devs list as shown below:
>
> static void calc_cached_dev_sectors(struct cache_set *c)
> {
> ...
>          list_for_each_entry(dc, &c->cached_devs, list)
>                  sectors += bdev_sectors(dc->bdev);
>
>          c->cached_dev_sectors = sectors;
> }
>
> But cached_dev won't be unlinked from c->cached_devs list until we call
> following list_move(&dc->list, &uncached_devices),
> so previous fix in 'commit 46010141da6677b81cc77f9b47f8ac62bd1cbfd3
> ("bcache: recal cached_dev_sectors on detach")' is wrong, now we move
> it to its right palce.
>
> Signed-off-by: Lin Feng <linf@...gsu.com>

Nice catch! I added it in my testing series. Thanks.

Coly Li

> ---
>   drivers/md/bcache/super.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index f2874c77ff79..8543e6997770 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1154,9 +1154,9 @@ static void cached_dev_detach_finish(struct work_struct *w)
>   
>   	mutex_lock(&bch_register_lock);
>   
> -	calc_cached_dev_sectors(dc->disk.c);
>   	bcache_device_detach(&dc->disk);
>   	list_move(&dc->list, &uncached_devices);
> +	calc_cached_dev_sectors(dc->disk.c);
>   
>   	clear_bit(BCACHE_DEV_DETACHING, &dc->disk.flags);
>   	clear_bit(BCACHE_DEV_UNLINK_DONE, &dc->disk.flags);