[PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

[PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

[Lukas Bulwahn]

make clang-analyzer caught my attention with:

  kernel/sysctl.c:1511:4: warning: Value stored to 'first' is never read \
  [clang-analyzer-deadcode.DeadStores]
                          first = 0;
                          ^

Commit 9f977fb7ae9d ("sysctl: add proc_do_large_bitmap") introduced
proc_do_large_bitmap(), where the variable first is only effectively used
when write is false; when write is true, the variable first is only used in
a dead assignment.

So, simply remove this dead assignment and put the variable in local scope.

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>
---
applies cleanly on v5.10-rc3 and next-20201106

Luis, Kees, Iurii, please pick this minor non-urgent clean-up patch.

 kernel/sysctl.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index ce75c67572b9..cc274a431d91 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1423,7 +1423,6 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
 			 void *buffer, size_t *lenp, loff_t *ppos)
 {
 	int err = 0;
-	bool first = 1;
 	size_t left = *lenp;
 	unsigned long bitmap_len = table->maxlen;
 	unsigned long *bitmap = *(unsigned long **) table->data;
@@ -1508,12 +1507,12 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
 			}
 
 			bitmap_set(tmp_bitmap, val_a, val_b - val_a + 1);
-			first = 0;
 			proc_skip_char(&p, &left, '\n');
 		}
 		left += skipped;
 	} else {
 		unsigned long bit_a, bit_b = 0;
+		bool first = 1;
 
 		while (left) {
 			bit_a = find_next_bit(bitmap, bitmap_len, bit_b);
-- 
2.17.1

Re: [PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

[Nathan Chancellor]

On Mon, Nov 09, 2020 at 08:11:07AM +0100, Lukas Bulwahn wrote:
> make clang-analyzer caught my attention with:
> 
>   kernel/sysctl.c:1511:4: warning: Value stored to 'first' is never read \
>   [clang-analyzer-deadcode.DeadStores]
>                           first = 0;
>                           ^
> 
> Commit 9f977fb7ae9d ("sysctl: add proc_do_large_bitmap") introduced
> proc_do_large_bitmap(), where the variable first is only effectively used
> when write is false; when write is true, the variable first is only used in
> a dead assignment.
> 
> So, simply remove this dead assignment and put the variable in local scope.
> 
> 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: Nathan Chancellor <natechancellor@gmail.com>

> ---
> applies cleanly on v5.10-rc3 and next-20201106
> 
> Luis, Kees, Iurii, please pick this minor non-urgent clean-up patch.
> 
>  kernel/sysctl.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ce75c67572b9..cc274a431d91 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1423,7 +1423,6 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
>  			 void *buffer, size_t *lenp, loff_t *ppos)
>  {
>  	int err = 0;
> -	bool first = 1;
>  	size_t left = *lenp;
>  	unsigned long bitmap_len = table->maxlen;
>  	unsigned long *bitmap = *(unsigned long **) table->data;
> @@ -1508,12 +1507,12 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
>  			}
>  
>  			bitmap_set(tmp_bitmap, val_a, val_b - val_a + 1);
> -			first = 0;
>  			proc_skip_char(&p, &left, '\n');
>  		}
>  		left += skipped;
>  	} else {
>  		unsigned long bit_a, bit_b = 0;
> +		bool first = 1;
>  
>  		while (left) {
>  			bit_a = find_next_bit(bitmap, bitmap_len, bit_b);
> -- 
> 2.17.1
> 

Re: [PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

[Tom Rix]

On 11/8/20 11:11 PM, Lukas Bulwahn wrote:
> make clang-analyzer caught my attention with:
>
>   kernel/sysctl.c:1511:4: warning: Value stored to 'first' is never read \
>   [clang-analyzer-deadcode.DeadStores]
>                           first = 0;
>                           ^
>
> Commit 9f977fb7ae9d ("sysctl: add proc_do_large_bitmap") introduced
> proc_do_large_bitmap(), where the variable first is only effectively used
> when write is false; when write is true, the variable first is only used in
> a dead assignment.
>
> So, simply remove this dead assignment and put the variable in local scope.
>
> 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>
> ---
> applies cleanly on v5.10-rc3 and next-20201106
>
> Luis, Kees, Iurii, please pick this minor non-urgent clean-up patch.
>
>  kernel/sysctl.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index ce75c67572b9..cc274a431d91 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1423,7 +1423,6 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
>  			 void *buffer, size_t *lenp, loff_t *ppos)
>  {
>  	int err = 0;
> -	bool first = 1;
>  	size_t left = *lenp;
>  	unsigned long bitmap_len = table->maxlen;
>  	unsigned long *bitmap = *(unsigned long **) table->data;
> @@ -1508,12 +1507,12 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
>  			}
>  
>  			bitmap_set(tmp_bitmap, val_a, val_b - val_a + 1);
> -			first = 0;
>  			proc_skip_char(&p, &left, '\n');
>  		}
>  		left += skipped;
>  	} else {
>  		unsigned long bit_a, bit_b = 0;
> +		bool first = 1;

This looks fine, but while you are here how about setting, to match the type

first = true

And then only clearing first once

if (!first)                                                                            
  proc_put_char(&buffer, &left, ',');

else

  first = false

Instead of at every loop iteraction

Tom

>  
>  		while (left) {
>  			bit_a = find_next_bit(bitmap, bitmap_len, bit_b);

Re: [PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

[Luis Chamberlain]

On Mon, Nov 09, 2020 at 05:26:37PM -0800, Tom Rix wrote:
> 
> On 11/8/20 11:11 PM, Lukas Bulwahn wrote:
> > make clang-analyzer caught my attention with:
> >
> >   kernel/sysctl.c:1511:4: warning: Value stored to 'first' is never read \
> >   [clang-analyzer-deadcode.DeadStores]
> >                           first = 0;
> >                           ^
> >
> > Commit 9f977fb7ae9d ("sysctl: add proc_do_large_bitmap") introduced
> > proc_do_large_bitmap(), where the variable first is only effectively used
> > when write is false; when write is true, the variable first is only used in
> > a dead assignment.
> >
> > So, simply remove this dead assignment and put the variable in local scope.
> >
> > 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>
> > ---
> > applies cleanly on v5.10-rc3 and next-20201106
> >
> > Luis, Kees, Iurii, please pick this minor non-urgent clean-up patch.
> >
> >  kernel/sysctl.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> > index ce75c67572b9..cc274a431d91 100644
> > --- a/kernel/sysctl.c
> > +++ b/kernel/sysctl.c
> > @@ -1423,7 +1423,6 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
> >  			 void *buffer, size_t *lenp, loff_t *ppos)
> >  {
> >  	int err = 0;
> > -	bool first = 1;
> >  	size_t left = *lenp;
> >  	unsigned long bitmap_len = table->maxlen;
> >  	unsigned long *bitmap = *(unsigned long **) table->data;
> > @@ -1508,12 +1507,12 @@ int proc_do_large_bitmap(struct ctl_table *table, int write,
> >  			}
> >  
> >  			bitmap_set(tmp_bitmap, val_a, val_b - val_a + 1);
> > -			first = 0;
> >  			proc_skip_char(&p, &left, '\n');
> >  		}
> >  		left += skipped;
> >  	} else {
> >  		unsigned long bit_a, bit_b = 0;
> > +		bool first = 1;
> 
> This looks fine, but while you are here how about setting, to match the type
> 
> first = true
> 
> And then only clearing first once
> 
> if (!first)                                                                            
>   proc_put_char(&buffer, &left, ',');
> 
> else
> 
>   first = false
> 
> Instead of at every loop iteraction

Thanks for your patch Lukas!

Agreed, please resend with that change as requested by Tom. And also
please add Andrew Morton <akpm@linux-foundation.org> to your To address.

  Luis