linux-kernel - Re: [PATCH v1] bcache: fix AB-BA deadlock between cache register and cache_set

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Message-ID: <b97d4326-3ce7-63d2-e4b6-8fbd27335fce@suse.de>
Date:   Fri, 8 Apr 2022 00:30:47 +0800
From:   Coly Li <colyli@...e.de>
To:     daihuaigang129@....com
Cc:     linux-bcache@...r.kernel.org, kent.overstreet@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] bcache: fix AB-BA deadlock between cache register and
 cache_set_free

On 3/29/22 11:17 AM, daihuaigang129@....com wrote:
> From: daihuaigang <daihuaigang129@....com>
>
> bcache register add kobject_mutex then bch_register_mutex,
> cache_set_free add bch_register_mutex then kobject_mutex.
> fix AB-BA deadlock between cache register and cache_set_free.

Can you explain a bit more about,

- For "bcache register add kobject_mutex", which function referred by 
"bcache register add", and where is the kobject_mutex.

- Where is bch_regsiter_mutex.

It is not clear for me to understand how hte AB-BA deadlock generated yet.

Thanks.


Coly Li


>
> Signed-off-by: daihuaigang <daihuaigang129@....com>
> ---
>   drivers/md/bcache/super.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index bf3de14..f17953c 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -1690,10 +1690,8 @@ static void cache_set_free(struct closure *cl)
>   	if (ca) {
>   		ca->set = NULL;
>   		c->cache = NULL;
> -		kobject_put(&ca->kobj);
>   	}
>   
> -
>   	if (c->moving_gc_wq)
>   		destroy_workqueue(c->moving_gc_wq);
>   	bioset_exit(&c->bio_split);
> @@ -1704,6 +1702,8 @@ static void cache_set_free(struct closure *cl)
>   
>   	list_del(&c->list);
>   	mutex_unlock(&bch_register_lock);
> +	if (ca)
> +		kobject_put(&ca->kobj);
>   
>   	pr_info("Cache set %pU unregistered\n", c->set_uuid);
>   	wake_up(&unregister_wait);