[RFC PATCH 1/6] trace/stack: Move code to save the stack trace into a separate function

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

In preparation to add support for stack tracer to powerpc, move code to
save stack trace and to calculate the frame sizes into a separate weak
function. Also provide access to some of the data structures used by the
stack trace code so that architectures can update those.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 include/linux/ftrace.h     |  8 ++++
 kernel/trace/trace_stack.c | 98 ++++++++++++++++++++------------------
 2 files changed, 60 insertions(+), 46 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index a69f363b61bf73..8263427379f05c 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -368,10 +368,18 @@ static inline void arch_ftrace_set_direct_caller(struct pt_regs *regs,
 
 #ifdef CONFIG_STACK_TRACER
 
+#define STACK_TRACE_ENTRIES 500
+
+extern unsigned long stack_dump_trace[STACK_TRACE_ENTRIES];
+extern unsigned stack_trace_index[STACK_TRACE_ENTRIES];
+extern unsigned int stack_trace_nr_entries;
+extern unsigned long stack_trace_max_size;
 extern int stack_tracer_enabled;
 
 int stack_trace_sysctl(struct ctl_table *table, int write, void *buffer,
 		       size_t *lenp, loff_t *ppos);
+void stack_get_trace(unsigned long traced_ip, unsigned long *stack_ref,
+					unsigned long stack_size, int *tracer_frame);
 
 /* DO NOT MODIFY THIS VARIABLE DIRECTLY! */
 DECLARE_PER_CPU(int, disable_stack_tracer);
diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 63c28504205162..5b63dbd37c8c25 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -19,13 +19,11 @@
 
 #include "trace.h"
 
-#define STACK_TRACE_ENTRIES 500
+unsigned long stack_dump_trace[STACK_TRACE_ENTRIES];
+unsigned stack_trace_index[STACK_TRACE_ENTRIES];
 
-static unsigned long stack_dump_trace[STACK_TRACE_ENTRIES];
-static unsigned stack_trace_index[STACK_TRACE_ENTRIES];
-
-static unsigned int stack_trace_nr_entries;
-static unsigned long stack_trace_max_size;
+unsigned int stack_trace_nr_entries;
+unsigned long stack_trace_max_size;
 static arch_spinlock_t stack_trace_max_lock =
 	(arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
 
@@ -152,49 +150,19 @@ static void print_max_stack(void)
  * Although the entry function is not displayed, the first function (sys_foo)
  * will still include the stack size of it.
  */
-static void check_stack(unsigned long ip, unsigned long *stack)
+void __weak stack_get_trace(unsigned long traced_ip, unsigned long *stack_ref,
+					unsigned long stack_size, int *tracer_frame)
 {
-	unsigned long this_size, flags; unsigned long *p, *top, *start;
-	static int tracer_frame;
-	int frame_size = READ_ONCE(tracer_frame);
+	unsigned long *p, *top, *start;
 	int i, x;
 
-	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
-	this_size = THREAD_SIZE - this_size;
-	/* Remove the frame of the tracer */
-	this_size -= frame_size;
-
-	if (this_size <= stack_trace_max_size)
-		return;
-
-	/* we do not handle interrupt stacks yet */
-	if (!object_is_on_stack(stack))
-		return;
-
-	/* Can't do this from NMI context (can cause deadlocks) */
-	if (in_nmi())
-		return;
-
-	local_irq_save(flags);
-	arch_spin_lock(&stack_trace_max_lock);
-
-	/* In case another CPU set the tracer_frame on us */
-	if (unlikely(!frame_size))
-		this_size -= tracer_frame;
-
-	/* a race could have already updated it */
-	if (this_size <= stack_trace_max_size)
-		goto out;
-
-	stack_trace_max_size = this_size;
-
 	stack_trace_nr_entries = stack_trace_save(stack_dump_trace,
 					       ARRAY_SIZE(stack_dump_trace) - 1,
 					       0);
 
 	/* Skip over the overhead of the stack tracer itself */
 	for (i = 0; i < stack_trace_nr_entries; i++) {
-		if (stack_dump_trace[i] == ip)
+		if (stack_dump_trace[i] == traced_ip)
 			break;
 	}
 
@@ -209,7 +177,7 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 	 * Now find where in the stack these are.
 	 */
 	x = 0;
-	start = stack;
+	start = stack_ref;
 	top = (unsigned long *)
 		(((unsigned long)start & ~(THREAD_SIZE-1)) + THREAD_SIZE);
 
@@ -223,7 +191,7 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 	while (i < stack_trace_nr_entries) {
 		int found = 0;
 
-		stack_trace_index[x] = this_size;
+		stack_trace_index[x] = stack_size;
 		p = start;
 
 		for (; p < top && i < stack_trace_nr_entries; p++) {
@@ -233,7 +201,7 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 			 */
 			if ((READ_ONCE_NOCHECK(*p)) == stack_dump_trace[i]) {
 				stack_dump_trace[x] = stack_dump_trace[i++];
-				this_size = stack_trace_index[x++] =
+				stack_size = stack_trace_index[x++] =
 					(top - p) * sizeof(unsigned long);
 				found = 1;
 				/* Start the search from here */
@@ -245,10 +213,10 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 				 * out what that is, then figure it out
 				 * now.
 				 */
-				if (unlikely(!tracer_frame)) {
-					tracer_frame = (p - stack) *
+				if (unlikely(!*tracer_frame)) {
+					*tracer_frame = (p - stack_ref) *
 						sizeof(unsigned long);
-					stack_trace_max_size -= tracer_frame;
+					stack_trace_max_size -= *tracer_frame;
 				}
 			}
 		}
@@ -272,6 +240,44 @@ static void check_stack(unsigned long ip, unsigned long *stack)
 #endif
 
 	stack_trace_nr_entries = x;
+}
+
+static void check_stack(unsigned long ip, unsigned long *stack)
+{
+	unsigned long this_size, flags;
+	static int tracer_frame;
+	int frame_size = READ_ONCE(tracer_frame);
+
+	this_size = ((unsigned long)stack) & (THREAD_SIZE-1);
+	this_size = THREAD_SIZE - this_size;
+	/* Remove the frame of the tracer */
+	this_size -= frame_size;
+
+	if (this_size <= stack_trace_max_size)
+		return;
+
+	/* we do not handle interrupt stacks yet */
+	if (!object_is_on_stack(stack))
+		return;
+
+	/* Can't do this from NMI context (can cause deadlocks) */
+	if (in_nmi())
+		return;
+
+	local_irq_save(flags);
+	arch_spin_lock(&stack_trace_max_lock);
+
+	/* In case another CPU set the tracer_frame on us */
+	if (unlikely(!frame_size))
+		this_size -= tracer_frame;
+
+	/* a race could have already updated it */
+	if (this_size <= stack_trace_max_size)
+		goto out;
+
+	stack_trace_max_size = this_size;
+
+	stack_get_trace(ip, stack, this_size, &tracer_frame);
 
 	if (task_stack_end_corrupted(current)) {
 		print_max_stack();
-- 
2.30.2