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 <[email protected]>
---
applies cleanly on current master and next-20201105
Balbir, please pick this minor non-urgent clean-up patch.
kernel/taskstats.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index a2802b6ff4bb..bd18a7bf5276 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
On Fri, Nov 06, 2020 at 07:22:10AM +0100, Lukas Bulwahn 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.
>
> Signed-off-by: Lukas Bulwahn <[email protected]>
Question below.
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> applies cleanly on current master and next-20201105
>
> Balbir, please pick this minor non-urgent clean-up patch.
>
> kernel/taskstats.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> index a2802b6ff4bb..bd18a7bf5276 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) {
Would it be worth moving the scope of rc into the for loop, now that it
is only used there? Looks like it used to be used in the main function
scope before commit 053c095a82cf ("netlink: make nlmsg_end() and
genlmsg_end() void") but if this is removed, it is only used to check
the return of genlmsg_unicast within the list_for_each_entry loop. Not
sure that buys us anything but I know you have done it in patches
before so I thought it was worth considering.
> skb_next = NULL;
> --
> 2.17.1
>
Cheers,
Nathan
On Fri, 6 Nov 2020, Nathan Chancellor wrote:
> On Fri, Nov 06, 2020 at 07:22:10AM +0100, Lukas Bulwahn 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.
> >
> > Signed-off-by: Lukas Bulwahn <[email protected]>
>
> Question below.
>
> Reviewed-by: Nathan Chancellor <[email protected]>
>
> > ---
> > applies cleanly on current master and next-20201105
> >
> > Balbir, please pick this minor non-urgent clean-up patch.
> >
> > kernel/taskstats.c | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> > index a2802b6ff4bb..bd18a7bf5276 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) {
>
> Would it be worth moving the scope of rc into the for loop, now that it
> is only used there? Looks like it used to be used in the main function
> scope before commit 053c095a82cf ("netlink: make nlmsg_end() and
> genlmsg_end() void") but if this is removed, it is only used to check
> the return of genlmsg_unicast within the list_for_each_entry loop. Not
> sure that buys us anything but I know you have done it in patches
> before so I thought it was worth considering.
>
I thought about moving it into the local scope, but it is a purely
cosmetic matter. Compilers are smart enough to generate the same code no
matter where it is defined.
So, I always look around in the same file to determine if there is some
kind of strong preference for very locally scoped variable definition or
if they are generally just all defined at the function entry.
Depending on my gut feeling in which style the file has mainly been
written, I then go with the one or other option. In this case, I went
with just keeping the definition at the function entry.
There is really no strong rule, though, that I see serving as good
indicator.
Thanks for your review.
Lukas
On Fri, 6 Nov 2020, Lukas Bulwahn wrote:
>
>
> On Fri, 6 Nov 2020, Nathan Chancellor wrote:
>
> > On Fri, Nov 06, 2020 at 07:22:10AM +0100, Lukas Bulwahn 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.
> > >
> > > Signed-off-by: Lukas Bulwahn <[email protected]>
> >
> > Question below.
> >
> > Reviewed-by: Nathan Chancellor <[email protected]>
> >
> > > ---
> > > applies cleanly on current master and next-20201105
> > >
> > > Balbir, please pick this minor non-urgent clean-up patch.
> > >
> > > kernel/taskstats.c | 1 -
> > > 1 file changed, 1 deletion(-)
> > >
> > > diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> > > index a2802b6ff4bb..bd18a7bf5276 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) {
> >
> > Would it be worth moving the scope of rc into the for loop, now that it
> > is only used there? Looks like it used to be used in the main function
> > scope before commit 053c095a82cf ("netlink: make nlmsg_end() and
> > genlmsg_end() void") but if this is removed, it is only used to check
> > the return of genlmsg_unicast within the list_for_each_entry loop. Not
> > sure that buys us anything but I know you have done it in patches
> > before so I thought it was worth considering.
> >
>
> I thought about moving it into the local scope, but it is a purely
> cosmetic matter. Compilers are smart enough to generate the same code no
> matter where it is defined.
> So, I always look around in the same file to determine if there is some
> kind of strong preference for very locally scoped variable definition or
> if they are generally just all defined at the function entry.
>
> Depending on my gut feeling in which style the file has mainly been
> written, I then go with the one or other option. In this case, I went
> with just keeping the definition at the function entry.
>
> There is really no strong rule, though, that I see serving as good
> indicator.
>
> Thanks for your review.
>
More specifically, if I think rc should be only defined locally, I would
probably need to apply the same argument to skb_next in this function and
put that in local scope as well. That did not happen in the past, so I am
not going to change that now neither. Hence, the change stays minimal
invasive but and that is important: it makes clang-analyzer happy.
And a happy clang-analyzer will eventually point to real bugs :)
There are a few examples of dead store warnings that in the end really
point to missing or wrong paths in some functions...
Lukas
Hi Lukas,
On 06/11/2020 06:22, Lukas Bulwahn 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.
Might be better to remove 'rc' completely as it is only used for the if
condition now.
diff --git a/kernel/taskstats.c b/kernel/taskstats.c
index a2802b6ff4bb..63541f1ae04a 100644
--- a/kernel/taskstats.c
+++ b/kernel/taskstats.c
@@ -113,11 +113,10 @@ static void send_cpu_listeners(struct sk_buff *skb,
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);
- rc = 0;
down_read(&listeners->sem);
list_for_each_entry(s, &listeners->list, list) {
skb_next = NULL;
@@ -126,8 +125,8 @@ static void send_cpu_listeners(struct sk_buff *skb,
if (!skb_next)
break;
}
- rc = genlmsg_unicast(&init_net, skb_cur, s->pid);
- if (rc == -ECONNREFUSED) {
+ if (genlmsg_unicast(&init_net, skb_cur, s->pid) ==
+ -ECONNREFUSED) {
s->valid = 0;
delcount++;
}
--
Regards
Sudip