[PATCH 1/2] um: Fix call tracer and bug handler

[PATCH 1/2] um: Fix call tracer and bug handler

[Richard Weinberger]

Commit 1de1502c (x86, um: now we can get rid of trivial uml headers)
removed accidentally bug.h which broke UML's call tracer and
bug handler.
Without asm-generic/bug.h UML uses BUG() from arch/x86/
which makes use of ud2.
UML cannot use ud2, it raises SIGILL in user mode.
As UML has a different stack for handling signals the call trace
will be cut off.

Reported-by: Sergei Trofimovich <slyich@gmail.com>
Tested-by: Sergei Trofimovich <slyich@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
---
 arch/um/include/asm/bug.h |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
 create mode 100644 arch/um/include/asm/bug.h

diff --git a/arch/um/include/asm/bug.h b/arch/um/include/asm/bug.h
new file mode 100644
index 0000000..9e33b86
--- /dev/null
+++ b/arch/um/include/asm/bug.h
@@ -0,0 +1,6 @@
+#ifndef __UM_BUG_H
+#define __UM_BUG_H
+
+#include <asm-generic/bug.h>
+
+#endif
-- 
1.6.6.1

[PATCH 2/2] um: Disable CONFIG_CMPXCHG_LOCAL

[Richard Weinberger]

Commit 8a5ec0ba "Lockless (and preemptless) fastpaths for slub"
makes use of this_cpu_cmpxchg_double() which needs
this_cpu_cmpxchg16b_emu() on x86_64.
Implementing cmpxchg16b emulation for UML would introduce
too much complexity. So just disable it.

LKML-Reference: <20110412192014.GF16342@mtj.dyndns.org>
Reported-by: Sergei Trofimovich <slyich@gmail.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
---
 arch/um/Kconfig.x86 |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/arch/um/Kconfig.x86 b/arch/um/Kconfig.x86
index 02fb017..a9da516 100644
--- a/arch/um/Kconfig.x86
+++ b/arch/um/Kconfig.x86
@@ -4,6 +4,10 @@ menu "UML-specific options"
 
 menu "Host processor type and features"
 
+config CMPXCHG_LOCAL
+	bool
+	default n
+
 source "arch/x86/Kconfig.cpu"
 
 endmenu
-- 
1.6.6.1

Re: [PATCH 2/2] um: Disable CONFIG_CMPXCHG_LOCAL

[Pekka Enberg]

On Wed, Apr 13, 2011 at 3:41 PM, Richard Weinberger <richard@nod.at> wrote:
> Commit 8a5ec0ba "Lockless (and preemptless) fastpaths for slub"
> makes use of this_cpu_cmpxchg_double() which needs
> this_cpu_cmpxchg16b_emu() on x86_64.
> Implementing cmpxchg16b emulation for UML would introduce
> too much complexity. So just disable it.
>
> LKML-Reference: <20110412192014.GF16342@mtj.dyndns.org>
> Reported-by: Sergei Trofimovich <slyich@gmail.com>
> Signed-off-by: Richard Weinberger <richard@nod.at>

Acked-by: Pekka Enberg <penberg@kernel.org>