[PATCH -tip 1/4] Text Edit Lock - Architecture Independent Code (v2)

[Masami Hiramatsu <mhiramat@redhat.com>]

From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

This is an architecture independant synchronization around kernel text
modifications through use of a global mutex.

A mutex has been chosen so that kprobes, the main user of this, can sleep during
memory allocation between the memory read of the instructions it must replace
and the memory write of the breakpoint.

Other user of this interface: immediate values.

Paravirt and alternatives are always done when SMP is inactive, so there is no
need to use locks.

Changelog :
Export text_mutex directly.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Andi Kleen <andi@firstfloor.org>
CC: Ingo Molnar <mingo@elte.hu>
---
 include/linux/memory.h |    6 ++++++
 mm/memory.c            |    9 +++++++++
 2 files changed, 15 insertions(+)

Index: 2.6.29-rc7/include/linux/memory.h
===================================================================
--- 2.6.29-rc7.orig/include/linux/memory.h
+++ 2.6.29-rc7/include/linux/memory.h
@@ -99,4 +99,10 @@ enum mem_add_context { BOOT, HOTPLUG };
 #define hotplug_memory_notifier(fn, pri) do { } while (0)
 #endif

+/*
+ * Kernel text modification mutex, used for code patching. Users of this lock
+ * can sleep.
+ */
+extern struct mutex text_mutex;
+
 #endif /* _LINUX_MEMORY_H_ */
Index: 2.6.29-rc7/mm/memory.c
===================================================================
--- 2.6.29-rc7.orig/mm/memory.c
+++ 2.6.29-rc7/mm/memory.c
@@ -48,6 +48,8 @@
 #include <linux/rmap.h>
 #include <linux/module.h>
 #include <linux/delayacct.h>
+#include <linux/kprobes.h>
+#include <linux/mutex.h>
 #include <linux/init.h>
 #include <linux/writeback.h>
 #include <linux/memcontrol.h>
@@ -99,6 +101,13 @@ int randomize_va_space __read_mostly =
 					2;
 #endif

+/*
+ * mutex protecting text section modification (dynamic code patching).
+ * some users need to sleep (allocating memory...) while they hold this lock.
+ */
+DEFINE_MUTEX(text_mutex);
+EXPORT_SYMBOL_GPL(text_mutex);
+
 static int __init disable_randmaps(char *s)
 {
 	randomize_va_space = 0;
-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com