linux-kernel - [PATCH 3.16.y-ckt 068/135] um: Skip futex_atomic_cmpxchg

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Date:	Fri,  6 Feb 2015 12:00:46 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Richard Weinberger <richard@....at>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 068/135] um: Skip futex_atomic_cmpxchg_inatomic() test

3.16.7-ckt6 -stable review patch.  If anyone has any objections, please let me know.

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

From: Richard Weinberger <richard@....at>

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@...redi.hu>
Suggested-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Signed-off-by: Richard Weinberger <richard@....at>
Tested-by: Daniel Walter <d.walter@...0.at>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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

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