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From:   Hans Holmberg <hans.ml.holmberg@owltronix.com>
Date:   Fri, 23 Nov 2018 11:04:58 +0100
Message-ID: <CANr-nt2XMzZnd309pY7QJxYXWMSuXXrcWMt8F=pa49BzARb5dg@mail.gmail.com>
Subject: Re: [PATCH] lightnvm: pblk: avoid ref warning on cache creation
To:     =?UTF-8?Q?Javier_Gonz=C3=A1lez?= <javier@javigon.com>
Cc:     Matias Bjorling <mb@lightnvm.io>,
        Hans Holmberg <hans.holmberg@cnexlabs.com>,
        linux-block@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Javier Gonzalez <javier@cnexlabs.com>
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Great catch Javier! Nice refactoring work too.

Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
On Thu, Nov 22, 2018 at 2:47 PM Javier Gonz=C3=A1lez <javier@javigon.com> w=
rote:
>
> The current kref implementation around pblk global caches triggers a
> false positive on refcount_inc_checked() (when called) as the kref is
> initialized to 0. Instead of usint kref_inc() on a 0 reference, which is
> in principle correct, use kref_init() to avoid the check. This is also
> more explicit about what actually happens on cache creation.
>
> In the process, do a small refactoring to use kref helpers.
>
> Signed-off-by: Javier Gonz=C3=A1lez <javier@cnexlabs.com>
> ---
>  drivers/lightnvm/pblk-init.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
> index 13822594647c..e225bd60cbb4 100644
> --- a/drivers/lightnvm/pblk-init.c
> +++ b/drivers/lightnvm/pblk-init.c
> @@ -350,23 +350,19 @@ static int pblk_create_global_caches(void)
>
>  static int pblk_get_global_caches(void)
>  {
> -       int ret;
> +       int ret =3D 0;
>
>         mutex_lock(&pblk_caches.mutex);
>
> -       if (kref_read(&pblk_caches.kref) > 0) {
> -               kref_get(&pblk_caches.kref);
> -               mutex_unlock(&pblk_caches.mutex);
> -               return 0;
> -       }
> +       if (kref_get_unless_zero(&pblk_caches.kref))
> +               goto out;
>
>         ret =3D pblk_create_global_caches();
> -
>         if (!ret)
> -               kref_get(&pblk_caches.kref);
> +               kref_init(&pblk_caches.kref);
>
> +out:
>         mutex_unlock(&pblk_caches.mutex);
> -
>         return ret;
>  }
>
> --
> 2.7.4
>