linux-kernel - Re: [PATCH] block/rnbd: Remove a useless mutex

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Date:   Mon, 7 Feb 2022 06:59:45 +0100
From:   Jinpu Wang <jinpu.wang@...os.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     "Md. Haris Iqbal" <haris.iqbal@...os.com>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH] block/rnbd: Remove a useless mutex

On Sun, Feb 6, 2022 at 10:19 AM Christophe JAILLET
<christophe.jaillet@...adoo.fr> wrote:
>
> According to lib/idr.c,
>    The IDA handles its own locking.  It is safe to call any of the IDA
>    functions without synchronisation in your code.
>
> so the 'ida_lock' mutex can just be removed.
> It is here only to protect some ida_simple_get()/ida_simple_remove() calls.
Hi Christophe,


 ida_simple_get() and ida_simple_remove() are deprecated. Use
 ida_alloc() and ida_free() instead respectively.

 While at it, can you convert the api too?

Thanks!
Jinpu Wang

>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/block/rnbd/rnbd-clt.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index 9a880d559ab8..eaff369eff36 100644
> --- a/drivers/block/rnbd/rnbd-clt.c
> +++ b/drivers/block/rnbd/rnbd-clt.c
> @@ -23,7 +23,6 @@ MODULE_LICENSE("GPL");
>
>  static int rnbd_client_major;
>  static DEFINE_IDA(index_ida);
> -static DEFINE_MUTEX(ida_lock);
>  static DEFINE_MUTEX(sess_lock);
>  static LIST_HEAD(sess_list);
>
> @@ -55,9 +54,7 @@ static void rnbd_clt_put_dev(struct rnbd_clt_dev *dev)
>         if (!refcount_dec_and_test(&dev->refcount))
>                 return;
>
> -       mutex_lock(&ida_lock);
>         ida_simple_remove(&index_ida, dev->clt_device_id);
> -       mutex_unlock(&ida_lock);
>         kfree(dev->hw_queues);
>         kfree(dev->pathname);
>         rnbd_clt_put_sess(dev->sess);
> @@ -1460,10 +1457,8 @@ static struct rnbd_clt_dev *init_dev(struct rnbd_clt_session *sess,
>                 goto out_alloc;
>         }
>
> -       mutex_lock(&ida_lock);
>         ret = ida_simple_get(&index_ida, 0, 1 << (MINORBITS - RNBD_PART_BITS),
>                              GFP_KERNEL);
> -       mutex_unlock(&ida_lock);
>         if (ret < 0) {
>                 pr_err("Failed to initialize device '%s' from session %s, allocating idr failed, err: %d\n",
>                        pathname, sess->sessname, ret);
> --
> 2.32.0
>