From: Nathan Chancellor <[email protected]>
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/aarch64-linux-android-4.9/
Cc: [email protected]
Fixes: 045afc24124d ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero
result value")
Reviewed-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Catalin Marinas <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
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
@@ -53,7 +53,7 @@
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();
