From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
stable@vger.kernel.org, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers
Date: Wed, 17 Apr 2019 11:01:02 +0200 [thread overview]
Message-ID: <20190417090102.GA11773@kroah.com> (raw)
In-Reply-To: <20190417072121.4450-1-natechancellor@gmail.com>
On Wed, Apr 17, 2019 at 12:21:21AM -0700, Nathan Chancellor wrote:
> Commit 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with
> non-zero result value") removed oldval's zero initialization in
> arch_futex_atomic_op_inuser because it is not necessary. Unfortunately,
> Android's arm64 GCC 4.9.4 [1] does not agree:
>
> ../kernel/futex.c: In function 'do_futex':
> ../kernel/futex.c:1658:17: warning: 'oldval' may be used uninitialized
> in this function [-Wmaybe-uninitialized]
> return oldval == cmparg;
> ^
> In file included from ../kernel/futex.c:73:0:
> ../arch/arm64/include/asm/futex.h:53:6: note: 'oldval' was declared here
> int oldval, ret, tmp;
> ^
>
> GCC fails to follow that when ret is non-zero, futex_atomic_op_inuser
> returns right away, avoiding the uninitialized use that it claims.
> Restoring the zero initialization works around this issue.
>
> [1]: https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/aarch64/aarch64-linux-android-4.9/
>
> Cc: stable@vger.kernel.org
> Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value")
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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next prev parent reply other threads:[~2019-04-17 9:01 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-17 7:21 [PATCH] arm64: futex: Restore oldval initialization to work around buggy compilers Nathan Chancellor
2019-04-17 9:01 ` Greg Kroah-Hartman [this message]
2019-04-17 9:53 ` Catalin Marinas
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