Re: [PATCH] block/rnbd-clt: improve find_or_create_sess() return check

[Nathan Chancellor <natechancellor@gmail.com>]

On Sun, Jan 10, 2021 at 01:57:26PM -0800, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> clang static analysis reports this problem
> 
> rnbd-clt.c:1212:11: warning: Branch condition evaluates to a
>   garbage value
>         else if (!first)
>                  ^~~~~~

Ah, is it complaining that the 'if (IS_ERR(sess)) {' section in
find_or_create_sess() does not initialize first even though that will be
caught by the 'if (sess == ERR_PTR(-ENOMEM))' in
find_and_get_or_create_sess() because alloc_sess() only returns an
-ENOMEM error pointer?

> 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@redhat.com>

Every maintainer has their preference for where and how stuff gets
initialized but this makes sense to me. I am not sure the commit above
find_or_create_sess() is needed but again, personal preference.

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
>  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
>