Commit 8242227e authored by Nathan Chancellor's avatar Nathan Chancellor Committed by Stefan Bader

arm64: futex: Restore oldval initialization to work around buggy compilers

BugLink: https://bugs.launchpad.net/bugs/1828420

commit ff8acf92 upstream.

Commit 045afc24 ("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: 045afc24 ("arm64: futex: Fix FUTEX_WAKE_OP atomic ops with non-zero result value")
Reviewed-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarKleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: default avatarStefan Bader <stefan.bader@canonical.com>
parent d4b4eec1
...@@ -55,7 +55,7 @@ ...@@ -55,7 +55,7 @@
static inline int static inline int
arch_futex_atomic_op_inuser(int op, int oparg, int *oval, u32 __user *uaddr) 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(); pagefault_disable();
......
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