[PATCH] fgraph: fix unused value in register_ftrace_graph()

[PATCH] fgraph: fix unused value in register_ftrace_graph()

[Gianfranco Trad]

Coverity reports unused assignment to value ret. [1]
ret is assigned to 0 here, but that stored value is overwritten before
it can be used. The overwrite might happen either at line 1277, 1290 
or eventually at line 1306. Therefore, cleanup the unused assignment.

[1] Coverity Scan, CID 1633338

Signed-off-by: Gianfranco Trad <gianf.trad@gmail.com>
---
 kernel/trace/fgraph.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 41e7a15dcb50..cc2e065c1c8d 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1262,7 +1262,6 @@ int register_ftrace_graph(struct fgraph_ops *gops)
 			return ret;
 		}
 		fgraph_initialized = true;
-		ret = 0;
 	}
 
 	if (!fgraph_array[0]) {
-- 
2.43.0

Re: [PATCH] fgraph: fix unused value in register_ftrace_graph()

[Steven Rostedt]

On Mon, 21 Oct 2024 12:24:29 +0200
Gianfranco Trad <gianf.trad@gmail.com> wrote:

> Coverity reports unused assignment to value ret. [1]
> ret is assigned to 0 here, but that stored value is overwritten before
> it can be used. The overwrite might happen either at line 1277, 1290 
> or eventually at line 1306. Therefore, cleanup the unused assignment.
> 
> [1] Coverity Scan, CID 1633338

What does the above mean? For such a simple change, is it really
unnecessary?

> 
> Signed-off-by: Gianfranco Trad <gianf.trad@gmail.com>
> ---
>  kernel/trace/fgraph.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 41e7a15dcb50..cc2e065c1c8d 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1262,7 +1262,6 @@ int register_ftrace_graph(struct fgraph_ops *gops)
>  			return ret;
>  		}
>  		fgraph_initialized = true;
> -		ret = 0;

Not to mention that if this is to go, why not get rid of the
declaration part too? That is:

-	int ret = 0;
+	int ret;

But still, this code is about to be merged with other code where this
change may cause issues. This is such a slow path that getting rid of
the extra initialization may not be worth it.

-- Steve


>  	}
>  
>  	if (!fgraph_array[0]) {

Re: [PATCH] fgraph: fix unused value in register_ftrace_graph()

[Gianfranco Trad]

--- Redirecting locally, forgot to cc mailing list ---

On 22/10/24 08:56, Steven Rostedt wrote:
> On Mon, 21 Oct 2024 12:24:29 +0200
> Gianfranco Trad <gianf.trad@gmail.com> wrote:
> 
>> Coverity reports unused assignment to value ret. [1]
>> ret is assigned to 0 here, but that stored value is overwritten before
>> it can be used. The overwrite might happen either at line 1277, 1290
>> or eventually at line 1306. Therefore, cleanup the unused assignment.
>>
>> [1] Coverity Scan, CID 1633338
> 
> What does the above mean? For such a simple change, is it really
> unnecessary?
> 

Static analyzer complains that ret is assigned again to 0 there (doesn't 
complain about the declaration phase in which it was already assigned to 
0) but no instructions later make use of this re-assigned value.
Therefore, it flags it as not needed assignment.

>> Signed-off-by: Gianfranco Trad <gianf.trad@gmail.com>
>> ---
>>   kernel/trace/fgraph.c | 1 -
>>   1 file changed, 1 deletion(-)
>>
>> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
>> index 41e7a15dcb50..cc2e065c1c8d 100644
>> --- a/kernel/trace/fgraph.c
>> +++ b/kernel/trace/fgraph.c
>> @@ -1262,7 +1262,6 @@ int register_ftrace_graph(struct fgraph_ops *gops)
>>   			return ret;
>>   		}
>>   		fgraph_initialized = true;
>> -		ret = 0;
> 
> Not to mention that if this is to go, why not get rid of the
> declaration part too? That is:
> 
> -	int ret = 0;
> +	int ret;
> 

I see this, but the static analyzer will actually complain if we get rid 
of int ret = 0 in the declaration phase here, saying something in the 
lines "ret uninitialized at declaration".
To recap, Coverity complains that after declaration ret is assigned 
again to 0 (line 1262) without using this specific re-assignment because 
later on instructions overwrite this value, before it is even used by 
any instruction.

> But still, this code is about to be merged with other code where this
> change may cause issues. This is such a slow path that getting rid of
> the extra initialization may not be worth it.
> 

Understood. This report by Coverity can be considered something trivial, 
so it's up to you what to do. Just wanted to report it and help.

Have a nice day,

-- Gian

> -- Steve
> 
> 
>>   	}
>>   
>>   	if (!fgraph_array[0]) {
>