[RFC][PATCH 4/5] tracepoints: Grab get_online_cpus() before taking tracepoints_mutex

[Steven Rostedt]

From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>

There's places that take tracepoints_mutex while holding get_online_cpus(),
and since tracepoints call jump_label code, which also takes
get_online_cpus(), make sure that the tracepoints_mutex is always taken
under get_online_cpus().

Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
---
 kernel/tracepoint.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 685c50ae6300..e41eab51b435 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -23,6 +23,7 @@
 #include <linux/rcupdate.h>
 #include <linux/tracepoint.h>
 #include <linux/err.h>
+#include <linux/cpu.h>
 #include <linux/slab.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/task.h>
@@ -276,12 +277,14 @@ int tracepoint_probe_register_prio(struct tracepoint *tp, void *probe,
 	struct tracepoint_func tp_func;
 	int ret;
 
+	get_online_cpus();
 	mutex_lock(&tracepoints_mutex);
 	tp_func.func = probe;
 	tp_func.data = data;
 	tp_func.prio = prio;
 	ret = tracepoint_add_func(tp, &tp_func, prio);
 	mutex_unlock(&tracepoints_mutex);
+	put_online_cpus();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(tracepoint_probe_register_prio);
@@ -318,11 +321,13 @@ int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
 	struct tracepoint_func tp_func;
 	int ret;
 
+	get_online_cpus();
 	mutex_lock(&tracepoints_mutex);
 	tp_func.func = probe;
 	tp_func.data = data;
 	ret = tracepoint_remove_func(tp, &tp_func);
 	mutex_unlock(&tracepoints_mutex);
+	put_online_cpus();
 	return ret;
 }
 EXPORT_SYMBOL_GPL(tracepoint_probe_unregister);
-- 
2.10.2