| Message ID | 20201109071107.22560-1-lukas.bulwahn@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sysctl: move local variable in proc_do_large_bitmap() to proper scope | expand |
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 >
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);
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
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);
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(-)