linux-kernel - Re: [PATCH v2] block/rnbd: Remove a useless mutex

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Date:   Tue, 8 Feb 2022 07:24:43 +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 v2] block/rnbd: Remove a useless mutex

On Mon, Feb 7, 2022 at 9:48 PM 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.
>
> While at it, switch to ida_alloc_XXX()/ida_free() instead to
> ida_simple_get()/ida_simple_remove().
> The latter is deprecated and more verbose.
>
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Acked-by: Jack Wang <jinpu.wang@...os.com>
Thanks!
> ---
>  drivers/block/rnbd/rnbd-clt.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index 9a880d559ab8..1f63f308eb39 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);
> +       ida_free(&index_ida, dev->clt_device_id);
>         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);
> +       ret = ida_alloc_max(&index_ida, 1 << (MINORBITS - RNBD_PART_BITS),
> +                           GFP_KERNEL);
>         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
>