3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Richard Weinberger <[email protected]>

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 <[email protected]>
Suggested-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>
Tested-by: Daniel Walter <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

---
 arch/um/Kconfig.common |    1 +
 1 file changed, 1 insertion(+)

--- 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


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