linux-kernel - [PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function

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Message-Id: <86b72f0c134367b214910b27b9a6dd3321af93bb.1565774657.git.christophe.leroy@c-s.fr>
Date:   Wed, 14 Aug 2019 09:25:52 +0000 (UTC)
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH] powerpc/futex: fix warning: 'oldval' may be used
 uninitialized in this function

  CC      kernel/futex.o
kernel/futex.c: In function 'do_futex':
kernel/futex.c:1676:17: warning: 'oldval' may be used uninitialized in this function [-Wmaybe-uninitialized]
   return oldval == cmparg;
                 ^
kernel/futex.c:1651:6: note: 'oldval' was declared here
  int oldval, ret;
      ^

This is because arch_futex_atomic_op_inuser() only sets *oval
if ret is NUL and GCC doesn't see that it will use it only when
ret is NUL.

Anyway, the non-NUL ret path is an error path that won't suffer from
setting *oval, and as *oval is a local var in futex_atomic_op_inuser()
it will have no impact.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
 arch/powerpc/include/asm/futex.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/futex.h b/arch/powerpc/include/asm/futex.h
index 3a6aa57b9d90..eea28ca679db 100644
--- a/arch/powerpc/include/asm/futex.h
+++ b/arch/powerpc/include/asm/futex.h
@@ -60,8 +60,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval,
 
 	pagefault_enable();
 
-	if (!ret)
-		*oval = oldval;
+	*oval = oldval;
 
 	prevent_write_to_user(uaddr, sizeof(*uaddr));
 	return ret;
-- 
2.13.3