commit 5ac9f62267dc92c7735c642a5942d9e6c1190308
author Steven Rostedt <rostedt@goodmis.org> Wed Mar 25 20:55:00 2009 -0400
committer Ingo Molnar <mingo@elte.hu> Tue Apr 07 14:00:39 2009 +0200
tree b426f4c02384d9454ee91ca7d5ab8a495bc679d0
parent 5f0c6c03c5fee91c02c696bc9bf4c0d41392abe7

function-graph: add proper initialization for init task

Impact: fix to crash going to kexec

The init task did not properly initialize the function graph pointers.
Altough these pointers are NULL, they can not be assumed to be NULL
for the init task, and must still be properly initialize.

This usually is not an issue since a problem only arises when a task
exits, and the init tasks do not usually exit. But when doing tests
with kexec, the init tasks do exit, and the bug appears.

This patch properly initializes the init tasks function graph data
structures.

Reported-and-Tested-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <alpine.DEB.2.00.0903252053080.5675@gandalf.stny.rr.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/ftrace.h

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 015a3d2..da5405d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -356,6 +356,9 @@
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 
+/* for init task */
+#define INIT_FTRACE_GRAPH		.ret_stack = NULL
+
 /*
  * Stack of return addresses for functions
  * of a thread.
@@ -430,10 +433,11 @@
 {
 	atomic_dec(&current->tracing_graph_pause);
 }
-#else
+#else /* !CONFIG_FUNCTION_GRAPH_TRACER */
 
 #define __notrace_funcgraph
 #define __irq_entry
+#define INIT_FTRACE_GRAPH
 
 static inline void ftrace_graph_init_task(struct task_struct *t) { }
 static inline void ftrace_graph_exit_task(struct task_struct *t) { }
@@ -445,7 +449,7 @@
 
 static inline void pause_graph_tracing(void) { }
 static inline void unpause_graph_tracing(void) { }
-#endif
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
 
 #ifdef CONFIG_TRACING
 #include <linux/sched.h>