tracing/kprobe: Wait for disabling all running kprobe handlers

Wait for disabling all running kprobe handlers when a kprobe
event is disabled, since the caller, trace_remove_event_call()
supposes that a removing event is disabled completely by
disabling the event.
With this change, ftrace can ensure that there is no running
event handlers after disabling it.

Link: http://lkml.kernel.org/r/20130709093526.20138.93100.stgit@mhiramat-M0-7522

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 17 insertions, 6 deletions

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index ae6ce835b023..3811487e7a7a 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -243,11 +243,11 @@ find_event_file_link(struct trace_probe *tp, struct ftrace_event_file *file)
 static int
 disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
 {
+        struct event_file_link *link = NULL;
+        int wait = 0;
         int ret = 0;
 
         if (file) {
-                struct event_file_link *link;
-
                 link = find_event_file_link(tp, file);
                 if (!link) {
                         ret = -EINVAL;
@@ -255,10 +255,7 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
                 }
 
                 list_del_rcu(&link->list);
-                /* synchronize with kprobe_trace_func/kretprobe_trace_func */
-                synchronize_sched();
-                kfree(link);
-
+                wait = 1;
                 if (!list_empty(&tp->files))
                         goto out;
 
@@ -271,8 +268,22 @@ disable_trace_probe(struct trace_probe *tp, struct ftrace_event_file *file)
                         disable_kretprobe(&tp->rp);
                 else
                         disable_kprobe(&tp->rp.kp);
+                wait = 1;
         }
  out:
+        if (wait) {
+                /*
+                 * Synchronize with kprobe_trace_func/kretprobe_trace_func
+                 * to ensure disabled (all running handlers are finished).
+                 * This is not only for kfree(), but also the caller,
+                 * trace_remove_event_call() supposes it for releasing
+                 * event_call related objects, which will be accessed in
+                 * the kprobe_trace_func/kretprobe_trace_func.
+                 */
+                synchronize_sched();
+                kfree(link);    /* Ignored if link == NULL */
+        }
+
         return ret;
 }