linux-kernel - [PATCH] sysctl: move local variable in proc_do_large

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Date:   Mon,  9 Nov 2020 08:11:07 +0100
From:   Lukas Bulwahn <lukas.bulwahn@...il.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>,
        linux-fsdevel@...r.kernel.org
Cc:     Tom Rix <trix@...hat.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com,
        kernel-janitors@...r.kernel.org, linux-safety@...ts.elisa.tech,
        linux-kernel@...r.kernel.org,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: [PATCH] sysctl: move local variable in proc_do_large_bitmap() to proper scope

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@...il.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