um: Skip futex_atomic_cmpxchg_inatomic() test

commit f911d731054ab3d82ee72a16b889e17ca3a2332a upstream.

futex_atomic_cmpxchg_inatomic() does not work on UML because
it triggers a copy_from_user() in kernel context.
On UML copy_from_user() can only be used if the kernel was called
by a real user space process such that UML can use ptrace()
to fetch the value.

Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Richard Weinberger <richard@nod.at>
Tested-by: Daniel Walter <d.walter@0x90.at>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index 6915d28cf118f6c406ff53b20802a36e6ddfcbe0..85a70c14d70f5cc2ad6b3d03bf794d9e29b959cf 100644 (file)
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -3,6 +3,7 @@ config UML
        default y
        select HAVE_ARCH_AUDITSYSCALL
        select HAVE_UID16
+       select HAVE_FUTEX_CMPXCHG if FUTEX
        select GENERIC_IRQ_SHOW
        select GENERIC_CPU_DEVICES
        select GENERIC_IO