[3.16.y-ckt stable] Patch "um: Skip futex_atomic_cmpxchg_inatomic() test" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    um: Skip futex_atomic_cmpxchg_inatomic() test

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt6.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2ae5571fd4ea42e8f72e0b7096014047783c2daa Mon Sep 17 00:00:00 2001
From: Richard Weinberger <richard at nod.at>
Date: Wed, 10 Dec 2014 13:53:51 +0100
Subject: 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 at szeredi.hu>
Suggested-by: Geert Uytterhoeven <geert at linux-m68k.org>
Signed-off-by: Richard Weinberger <richard at nod.at>
Tested-by: Daniel Walter <d.walter at 0x90.at>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/um/Kconfig.common | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index 6915d28cf118..85a70c14d70f 100644
--- 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
--
2.1.4