linux-kernel - Re: [PATCH] block/rnbd-clt: improve find_or_create

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Date:   Mon, 11 Jan 2021 07:57:05 +0100
From:   Jinpu Wang <jinpu.wang@...ud.ionos.com>
To:     Tom Rix <trix@...hat.com>,
        Nathan Chancellor <natechancellor@...il.com>
Cc:     Danil Kipnis <danil.kipnis@...ud.ionos.com>,
        Jens Axboe <axboe@...nel.dk>, ndesaulniers@...gle.com,
        linux-block <linux-block@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] block/rnbd-clt: improve find_or_create_sess() return check

On Sun, Jan 10, 2021 at 10:58 PM <trix@...hat.com> wrote:
>
> From: Tom Rix <trix@...hat.com>
>
> clang static analysis reports this problem
>
> rnbd-clt.c:1212:11: warning: Branch condition evaluates to a
>   garbage value
>         else if (!first)
>                  ^~~~~~
>
> This is triggered in the find_and_get_or_create_sess() call
> because the variable first is not initialized and the
> earlier check is specifically for
>
>         if (sess == ERR_PTR(-ENOMEM))
>
> This is false positive.
>
> But the if-check can be reduced by initializing first to
> false and then returning if the call to find_or_creat_sess()
> does not set it to true.  When it remains false, either
> sess will be valid or not.  The not case is caught by
> find_and_get_or_create_sess()'s caller rnbd_clt_map_device()
>
>         sess = find_and_get_or_create_sess(...);
>         if (IS_ERR(sess))
>                 return ERR_CAST(sess);
>
> Since find_and_get_or_create_sess() initializes first to false
> setting it in find_or_create_sess() is not needed.
>
> Signed-off-by: Tom Rix <trix@...hat.com>
Less LOC is better :)
Acked-by: Jack Wang <jinpu.wang@...ud.ionos.com>
Thanks Tom and Nathan!
> ---
>  drivers/block/rnbd/rnbd-clt.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index 96e3f9fe8241..251f747cf10d 100644
> --- a/drivers/block/rnbd/rnbd-clt.c
> +++ b/drivers/block/rnbd/rnbd-clt.c
> @@ -919,6 +919,7 @@ static struct rnbd_clt_session *__find_and_get_sess(const char *sessname)
>         return NULL;
>  }
>
> +/* caller is responsible for initializing 'first' to false */
>  static struct
>  rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
>  {
> @@ -934,8 +935,7 @@ rnbd_clt_session *find_or_create_sess(const char *sessname, bool *first)
>                 }
>                 list_add(&sess->list, &sess_list);
>                 *first = true;
> -       } else
> -               *first = false;
> +       }
>         mutex_unlock(&sess_lock);
>
>         return sess;
> @@ -1203,13 +1203,11 @@ find_and_get_or_create_sess(const char *sessname,
>         struct rnbd_clt_session *sess;
>         struct rtrs_attrs attrs;
>         int err;
> -       bool first;
> +       bool first = false;
>         struct rtrs_clt_ops rtrs_ops;
>
>         sess = find_or_create_sess(sessname, &first);
> -       if (sess == ERR_PTR(-ENOMEM))
> -               return ERR_PTR(-ENOMEM);
> -       else if (!first)
> +       if (!first)
>                 return sess;
>
>         if (!path_cnt) {
> --
> 2.27.0
>