tracing: Enable records during the module load

I was debuging some module using "function" and "function_graph" tracers and noticed, that if you load module after you enabled tracing, the module's hooks will convert only to NOP instructions. The attached patch enables modules' hooks if there's function trace allready on, thus allowing to trace module functions. Signed-off-by: Jiri Olsa <jolsa@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> LKML-Reference: <20091013203425.896285120@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>

tracing: Enable records during the module load
I was debuging some module using "function" and "function_graph" tracers and noticed, that if you load module after you enabled tracing, the module's hooks will convert only to NOP instructions. The attached patch enables modules' hooks if there's function trace allready on, thus allowing to trace module functions. Signed-off-by: Jiri Olsa <jolsa@redhat.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> LKML-Reference: <20091013203425.896285120@goodmis.org> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Jiri Olsa · Ingo Molnar
1 parent 756d17ee7e
Showing 1 changed file with 30 additions and 8 deletions Side-by-side Diff
kernel/trace/ftrace.c
@@ -1270,12 +1270,34 @@
 		ftrace_new_addrs = p->newlist;
 		p->flags = 0L;
  
-		/* convert record (i.e, patch mcount-call with NOP) */
-		if (ftrace_code_disable(mod, p)) {
-			p->flags |= FTRACE_FL_CONVERTED;
-			ftrace_update_cnt++;
-		} else
+		/*
+		 * Do the initial record convertion from mcount jump
+		 * to the NOP instructions.
+		 */
+		if (!ftrace_code_disable(mod, p)) {
 			ftrace_free_rec(p);
+			continue;
+		}
+
+		p->flags |= FTRACE_FL_CONVERTED;
+		ftrace_update_cnt++;
+
+		/*
+		 * If the tracing is enabled, go ahead and enable the record.
+		 *
+		 * The reason not to enable the record immediatelly is the
+		 * inherent check of ftrace_make_nop/ftrace_make_call for
+		 * correct previous instructions.  Making first the NOP
+		 * conversion puts the module to the correct state, thus
+		 * passing the ftrace_make_call check.
+		 */
+		if (ftrace_start_up) {
+			int failed = __ftrace_replace_code(p, 1);
+			if (failed) {
+				ftrace_bug(failed, p->ip);
+				ftrace_free_rec(p);
+			}
+		}
 	}
  
 	stop = ftrace_now(raw_smp_processor_id());
@@ -2609,7 +2631,7 @@
 	return 0;
 }
  
-static int ftrace_convert_nops(struct module *mod,
+static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
 {
@@ -2669,7 +2691,7 @@
 {
 	if (ftrace_disabled || start == end)
 		return;
-	ftrace_convert_nops(mod, start, end);
+	ftrace_process_locs(mod, start, end);
 }
  
 static int ftrace_module_notify(struct notifier_block *self,
@@ -2730,7 +2752,7 @@
  
 	last_ftrace_enabled = ftrace_enabled = 1;
  
-	ret = ftrace_convert_nops(NULL,
+	ret = ftrace_process_locs(NULL,
 				  __start_mcount_loc,
 				  __stop_mcount_loc);
...	...	@@ -1270,12 +1270,34 @@
1270	1270	ftrace_new_addrs = p->newlist;
1271	1271	p->flags = 0L;
1272	1272
1273		- /* convert record (i.e, patch mcount-call with NOP) */
1274		- if (ftrace_code_disable(mod, p)) {
1275		- p->flags \|= FTRACE_FL_CONVERTED;
1276		- ftrace_update_cnt++;
1277		- } else
	1273	+ /*
	1274	+ * Do the initial record convertion from mcount jump
	1275	+ * to the NOP instructions.
	1276	+ */
	1277	+ if (!ftrace_code_disable(mod, p)) {
1278	1278	ftrace_free_rec(p);
	1279	+ continue;
	1280	+ }
	1281	+
	1282	+ p->flags \|= FTRACE_FL_CONVERTED;
	1283	+ ftrace_update_cnt++;
	1284	+
	1285	+ /*
	1286	+ * If the tracing is enabled, go ahead and enable the record.
	1287	+ *
	1288	+ * The reason not to enable the record immediatelly is the
	1289	+ * inherent check of ftrace_make_nop/ftrace_make_call for
	1290	+ * correct previous instructions. Making first the NOP
	1291	+ * conversion puts the module to the correct state, thus
	1292	+ * passing the ftrace_make_call check.
	1293	+ */
	1294	+ if (ftrace_start_up) {
	1295	+ int failed = __ftrace_replace_code(p, 1);
	1296	+ if (failed) {
	1297	+ ftrace_bug(failed, p->ip);
	1298	+ ftrace_free_rec(p);
	1299	+ }
	1300	+ }
1279	1301	}
1280	1302
1281	1303	stop = ftrace_now(raw_smp_processor_id());
...	...	@@ -2609,7 +2631,7 @@
2609	2631	return 0;
2610	2632	}
2611	2633
2612		-static int ftrace_convert_nops(struct module *mod,
	2634	+static int ftrace_process_locs(struct module *mod,
2613	2635	unsigned long *start,
2614	2636	unsigned long *end)
2615	2637	{
...	...	@@ -2669,7 +2691,7 @@
2669	2691	{
2670	2692	if (ftrace_disabled \|\| start == end)
2671	2693	return;
2672		- ftrace_convert_nops(mod, start, end);
	2694	+ ftrace_process_locs(mod, start, end);
2673	2695	}
2674	2696
2675	2697	static int ftrace_module_notify(struct notifier_block *self,
...	...	@@ -2730,7 +2752,7 @@
2730	2752
2731	2753	last_ftrace_enabled = ftrace_enabled = 1;
2732	2754
2733		- ret = ftrace_convert_nops(NULL,
	2755	+ ret = ftrace_process_locs(NULL,
2734	2756	__start_mcount_loc,
2735	2757	__stop_mcount_loc);
2736	2758