[PATCH RESEND 2] taskstats: remove unneeded dead assignment

[PATCH RESEND 2] taskstats: remove unneeded dead assignment

[Lukas Bulwahn]

make clang-analyzer on x86_64 defconfig caught my attention with:

  kernel/taskstats.c:120:2: warning: Value stored to 'rc' is never read \
  [clang-analyzer-deadcode.DeadStores]
          rc = 0;
          ^

Commit d94a041519f3 ("taskstats: free skb, avoid returns in
send_cpu_listeners") made send_cpu_listeners() not return a value and
hence, the rc variable remained only to be used within the loop where
it is always assigned before read and it does not need any other
initialisation.

So, simply remove this unneeded dead initializing assignment.

As compilers will detect this unneeded assignment and optimize this anyway,
the resulting object code is identical before and after this change.

No functional change. No change to object code.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
---
added Nick's Reviewed tag from the first resend:
  https://lore.kernel.org/all/CAKwvOdk68xzVVCCGgdEDj3fSD9nwgh8=7zi6QGa-hhxweRibYQ@mail.gmail.com/

Andrew, please pick this minor non-urgent clean-up patch.

Balbir Singh, mentioned in MAINTAINERS, has not been active lately.

 kernel/taskstats.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index 2b4898b4752e..7cdf4018a9c5 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -117,7 +117,6 @@ static void send_cpu_listeners(struct sk_buff *skb,
 
 	genlmsg_end(skb, reply);
 
-	rc = 0;
 	down_read(&listeners->sem);
 	list_for_each_entry(s, &listeners->list, list) {
 		skb_next = NULL;
-- 
2.17.1

Re: [PATCH RESEND 2] taskstats: remove unneeded dead assignment

[Andrew Morton]

On Mon,  7 Mar 2022 10:39:42 +0100 Lukas Bulwahn <lukas.bulwahn@gmail.com> wrote:

> make clang-analyzer on x86_64 defconfig caught my attention with:
> 
>   kernel/taskstats.c:120:2: warning: Value stored to 'rc' is never read \
>   [clang-analyzer-deadcode.DeadStores]
>           rc = 0;
>           ^
> 
> Commit d94a041519f3 ("taskstats: free skb, avoid returns in
> send_cpu_listeners") made send_cpu_listeners() not return a value and
> hence, the rc variable remained only to be used within the loop where
> it is always assigned before read and it does not need any other
> initialisation.
> 
> So, simply remove this unneeded dead initializing assignment.
> 
> As compilers will detect this unneeded assignment and optimize this anyway,
> the resulting object code is identical before and after this change.
> 
> No functional change. No change to object code.
> 
> ...
>
> --- a/kernel/taskstats.c
> +++ b/kernel/taskstats.c
> @@ -117,7 +117,6 @@ static void send_cpu_listeners(struct sk_buff *skb,
>  
>  	genlmsg_end(skb, reply);
>  
> -	rc = 0;
>  	down_read(&listeners->sem);
>  	list_for_each_entry(s, &listeners->list, list) {
>  		skb_next = NULL;

Yup.  It would be better to also reduce the scope of `rc' so later code
can't go and read it uninitialized.

--- a/kernel/taskstats.c~taskstats-remove-unneeded-dead-assignment-fix
+++ a/kernel/taskstats.c
@@ -113,12 +113,14 @@ static void send_cpu_listeners(struct sk
 	struct listener *s, *tmp;
 	struct sk_buff *skb_next, *skb_cur = skb;
 	void *reply = genlmsg_data(genlhdr);
-	int rc, delcount = 0;
+	int delcount = 0;
 
 	genlmsg_end(skb, reply);
 
 	down_read(&listeners->sem);
 	list_for_each_entry(s, &listeners->list, list) {
+		int rc;
+
 		skb_next = NULL;
 		if (!list_is_last(&s->list, &listeners->list)) {
 			skb_next = skb_clone(skb_cur, GFP_KERNEL);
_

(we could just elimiate `rc' altogether, but I think the above is OK,
perhaps a little more readable).