ftrace: fix dyn ftrace filter

Impact: correct implementation of dyn ftrace filter

The old decisions made by the filter algorithm was complex and incorrect.
This lead to inconsistent enabling or disabling of functions when
the filter was used.

This patch simplifies that code and in doing so, corrects the usage
of the filters.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/ftrace.c

@@ -394,72 +394,62 @@ __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
 
 	ip = rec->ip;
 
-	if (ftrace_filtered && enable) {
 	/*
-		 * If filtering is on:
+	 * If this record is not to be traced and
+	 * it is not enabled then do nothing.
 	 *
-		 * If this record is set to be filtered and
-		 * is enabled then do nothing.
+	 * If this record is not to be traced and
+	 * it is enabled then disabled it.
 	 *
-		 * If this record is set to be filtered and
-		 * it is not enabled, enable it.
-		 *
-		 * If this record is not set to be filtered
-		 * and it is not enabled do nothing.
-		 *
-		 * If this record is set not to trace then
-		 * do nothing.
-		 *
-		 * If this record is set not to trace and
-		 * it is enabled then disable it.
-		 *
-		 * If this record is not set to be filtered and
-		 * it is enabled, disable it.
 	 */
-
-		fl = rec->flags & (FTRACE_FL_FILTER | FTRACE_FL_NOTRACE |
-				   FTRACE_FL_ENABLED);
-
-		if ((fl ==  (FTRACE_FL_FILTER | FTRACE_FL_ENABLED)) ||
-		    (fl ==  (FTRACE_FL_FILTER | FTRACE_FL_NOTRACE)) ||
-		    !fl || (fl == FTRACE_FL_NOTRACE))
+	if (rec->flags & FTRACE_FL_NOTRACE) {
+		if (rec->flags & FTRACE_FL_ENABLED)
+			rec->flags &= ~FTRACE_FL_ENABLED;
+		else
 			return 0;
 
+	} else if (ftrace_filtered && enable) {
 		/*
-		 * If it is enabled disable it,
-		 * otherwise enable it!
+		 * Filtering is on:
 		 */
-		if (fl & FTRACE_FL_ENABLED) {
-			enable = 0;
+
+		fl = rec->flags & (FTRACE_FL_FILTER | FTRACE_FL_ENABLED);
+
+		/* Record is filtered and enabled, do nothing */
+		if (fl == (FTRACE_FL_FILTER | FTRACE_FL_ENABLED))
+			return 0;
+
+		/* Record is not filtered and is not enabled do nothing */
+		if (!fl)
+			return 0;
+
+		/* Record is not filtered but enabled, disable it */
+		if (fl == FTRACE_FL_ENABLED)
 			rec->flags &= ~FTRACE_FL_ENABLED;
-		} else {
-			enable = 1;
+		else
+		/* Otherwise record is filtered but not enabled, enable it */
 			rec->flags |= FTRACE_FL_ENABLED;
-		}
 	} else {
+		/* Disable or not filtered */
 
 		if (enable) {
-			/*
-			 * If this record is set not to trace and is
-			 * not enabled, do nothing.
-			 */
-			fl = rec->flags & (FTRACE_FL_NOTRACE | FTRACE_FL_ENABLED);
-			if (fl == FTRACE_FL_NOTRACE)
-				return 0;
-		}
-
-		if (enable) {
+			/* if record is enabled, do nothing */
 			if (rec->flags & FTRACE_FL_ENABLED)
 				return 0;
+
 			rec->flags |= FTRACE_FL_ENABLED;
+
 		} else {
+
+			/* if record is not enabled do nothing */
 			if (!(rec->flags & FTRACE_FL_ENABLED))
 				return 0;
+
 			rec->flags &= ~FTRACE_FL_ENABLED;
 		}
 	}
 
-	if (enable)
+	if (rec->flags & FTRACE_FL_ENABLED)
 		return ftrace_make_call(rec, FTRACE_ADDR);
 	else
 		return ftrace_make_nop(NULL, rec, FTRACE_ADDR);
@@ -554,7 +544,6 @@ static void ftrace_startup(void)
 
 	mutex_lock(&ftrace_start_lock);
 	ftrace_start_up++;
-	if (ftrace_start_up == 1)
 	command |= FTRACE_ENABLE_CALLS;
 
 	if (saved_ftrace_func != ftrace_trace_function) {