From: Richard Weinberger <richard@nod.at>
Date: Wed, 10 Dec 2014 12:53:51 +0000 (+0100)
Subject: um: Skip futex_atomic_cmpxchg_inatomic() test
X-Git-Tag: v3.12.37~50
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad63ddb0b121132417f91578791e88306396a41b;p=thirdparty%2Fkernel%2Fstable.git

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: Jiri Slaby <jslaby@suse.cz>
---

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index 8ddea1f8006a5..0228a6ab9b186 100644
--- a/arch/um/Kconfig.common
+++ b/arch/um/Kconfig.common
@@ -7,6 +7,7 @@ config UML
 	bool
 	default y
 	select HAVE_UID16
+	select HAVE_FUTEX_CMPXCHG if FUTEX
 	select GENERIC_IRQ_SHOW
 	select GENERIC_CPU_DEVICES
 	select GENERIC_IO