linux-kernel - [PATCH 3.18 176/183] um: Skip futex_atomic_cmpxchg

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Date:	Sun, 25 Jan 2015 10:08:18 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Miklos Szeredi <miklos@...redi.hu>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Richard Weinberger <richard@....at>,
	Daniel Walter <d.walter@...0.at>
Subject: [PATCH 3.18 176/183] um: Skip futex_atomic_cmpxchg_inatomic() test

3.18-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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 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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