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Message-ID: <878srt70fg.fsf@concordia.ellerman.id.au>
Date: Fri, 16 Aug 2019 22:35:31 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Christophe Leroy <christophe.leroy@....fr>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/futex: fix warning: 'oldval' may be used uninitialized in this function
Christophe Leroy <christophe.leroy@....fr> writes:
> 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
I prefer 0 to "NUL", as ret is an int. I'll reword it. But otherwise
this looks OK.
cheers
> 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
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