From: Nathan Chancellor natechancellor@gmail.com
commit ff8acf929014b7f87315588e0daf8597c8aa9d1c upstream.
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/aa...
Cc: stable@vger.kernel.org Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value") Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Nathan Chancellor natechancellor@gmail.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/include/asm/futex.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/arm64/include/asm/futex.h +++ b/arch/arm64/include/asm/futex.h @@ -55,7 +55,7 @@ static inline int arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr) { - int oldval, ret, tmp; + int oldval = 0, ret, tmp;
pagefault_disable();