linux-kernel - [PATCH] um: Skip futex_atomic_cmpxchg

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Message-Id: <1418216535-29295-1-git-send-email-richard@nod.at>
Date:	Wed, 10 Dec 2014 14:02:15 +0100
From:	Richard Weinberger <richard@....at>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	linux-kernel@...r.kernel.org, miklos@...redi.hu, lftan@...era.com,
	arnd@...db.de, geert@...ux-m68k.org,
	Richard Weinberger <richard@....at>
Subject: [PATCH] um: Skip futex_atomic_cmpxchg_inatomic() test

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

diff --git a/arch/um/Kconfig.common b/arch/um/Kconfig.common
index 87bc868..d195a87 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
-- 
2.1.0

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