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

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

[trix]

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)
                 ^~~~~~

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>
---
 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

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

[Nathan Chancellor]

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
> 

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

[Tom Rix]

On 1/10/21 9:14 PM, Nathan Chancellor wrote:
> 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?

Reviewing the code, failure looks like it returns only -ENOMEM.

So the check is correct but brittle.

>
>> 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.

Mostly this removes two unneeded branches at the cost of initializing a variable.

Secondary, the static analysis complaint is resolved.

Tom

>
> 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
>>

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

[Jinpu Wang]

On Sun, Jan 10, 2021 at 10:58 PM <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)
>                  ^~~~~~
>
> 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>
Less LOC is better :)
Acked-by: Jack Wang <jinpu.wang@cloud.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
>