[PATCH] fault-injection: Clamp debugfs stacktrace-depth to MAX_STACK_TRACE_DEPTH

Clamp /debug/fail*/stacktrace-depth to MAX_STACK_TRACE_DEPTH.  Ensures that a
read of /debug/fail*/stacktrace-depth always returns a truthful answer.
Signed-off-by: Don Mullis <dwm@meer.net>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

lib/fault-inject.c

@@ -53,6 +53,8 @@ static bool fail_task(struct fault_attr *attr, struct task_struct *task)
 	return !in_interrupt() && task->make_it_fail;
 }
 
+#define MAX_STACK_TRACE_DEPTH 32
+
 #ifdef CONFIG_STACK_UNWIND
 
 static asmlinkage int fail_stacktrace_callback(struct unwind_frame_info *info,
@@ -98,8 +100,7 @@ static bool fail_stacktrace(struct fault_attr *attr)
 
 	trace.nr_entries = 0;
 	trace.entries = entries;
-	trace.max_entries = (depth < MAX_STACK_TRACE_DEPTH) ?
-				depth : MAX_STACK_TRACE_DEPTH;
+	trace.max_entries = depth;
 	trace.skip = 1;
 	trace.all_contexts = 0;
 
@@ -179,6 +180,13 @@ static void debugfs_ul_set(void *data, u64 val)
 	*(unsigned long *)data = val;
 }
 
+static void debugfs_ul_set_MAX_STACK_TRACE_DEPTH(void *data, u64 val)
+{
+	*(unsigned long *)data =
+		val < MAX_STACK_TRACE_DEPTH ?
+		val : MAX_STACK_TRACE_DEPTH;
+}
+
 static u64 debugfs_ul_get(void *data)
 {
 	return *(unsigned long *)data;
@@ -192,6 +200,17 @@ static struct dentry *debugfs_create_ul(const char *name, mode_t mode,
 	return debugfs_create_file(name, mode, parent, value, &fops_ul);
 }
 
+DEFINE_SIMPLE_ATTRIBUTE(fops_ul_MAX_STACK_TRACE_DEPTH, debugfs_ul_get,
+			debugfs_ul_set_MAX_STACK_TRACE_DEPTH, "%llu\n");
+
+static struct dentry *debugfs_create_ul_MAX_STACK_TRACE_DEPTH(
+	const char *name, mode_t mode,
+	struct dentry *parent, unsigned long *value)
+{
+	return debugfs_create_file(name, mode, parent, value,
+				   &fops_ul_MAX_STACK_TRACE_DEPTH);
+}
+
 static void debugfs_atomic_t_set(void *data, u64 val)
 {
 	atomic_set((atomic_t *)data, val);
@@ -284,8 +303,8 @@ int init_fault_attr_dentries(struct fault_attr *attr, const char *name)
 						mode, dir, &attr->task_filter);
 
 	attr->dentries.stacktrace_depth_file =
-		debugfs_create_ul("stacktrace-depth", mode, dir,
-				  &attr->stacktrace_depth);
+		debugfs_create_ul_MAX_STACK_TRACE_DEPTH(
+			"stacktrace-depth", mode, dir, &attr->stacktrace_depth);
 
 	attr->dentries.require_start_file =
 		debugfs_create_ul("require-start", mode, dir, &attr->require_start);