Re: [PATCH -v3 6/7] kexec jump: __ftrace_enabled_save/restore

On Tue, Aug 12, 2008 at 11:14:36AM +0800, Huang Ying wrote:
Add __ftrace_enabled_save/restore, used to disable ftrace for a
while. Now, this is used by kexec jump, which need a version without
lock, for general situation, a locked version should be used.

Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx>

---
include/linux/ftrace.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)

--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -98,6 +98,27 @@ static inline void tracer_disable(void)
#endif
}

+/* Ftrace disable/restore without lock. Some synchronization mechanism
+ * must be used to prevent ftrace_enabled to be changed between
+ * disable/restore. */
+static inline int __ftrace_enabled_save(void)
+{
+#ifdef CONFIG_FTRACE
+ int saved_ftrace_enabled = ftrace_enabled;
+ ftrace_enabled = 0;
+ return saved_ftrace_enabled;
+#else
+ return 0;
+#endif
+}
+
+static inline void __ftrace_enabled_restore(int enabled)
+{
+#ifdef CONFIG_FTRACE
+ ftrace_enabled = enabled;
+#endif
+}
+
#ifdef CONFIG_FRAME_POINTER
/* TODO: need to fix this for ARM */
# define CALLER_ADDR0 ((unsigned long)__builtin_return_address(0))

I guess steven would like to see a patch which introduces both locked
and lockless versions and with a very good comment explaining in what
kind of unusual situation one can use the lockless version.

Thanks
Vivek
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