tracing: tprobe-events: Fix to register tracepoint correctly

Since __tracepoint_user_init() calls tracepoint_user_register() without
initializing tuser->tpoint with given tracpoint, it does not register
tracepoint stub function as callback correctly, and tprobe does not work.

Initializing tuser->tpoint correctly before tracepoint_user_register()
so that it sets up tracepoint callback.

I confirmed below example works fine again.

echo "t sched_switch preempt prev_pid=prev->pid next_pid=next->pid" > /sys/kernel/tracing/dynamic_events
echo 1 > /sys/kernel/tracing/events/tracepoints/sched_switch/enable
cat /sys/kernel/tracing/trace_pipe

Link: https://lore.kernel.org/all/176244793514.155515.6466348656998627773.stgit@devnote2/
Fixes: 2867495dea86 ("tracing: tprobe-events: Register tracepoint when enable tprobe event")
Reported-by: Beau Belgrave <beaub@linux.microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Tested-by: Beau Belgrave <beaub@linux.microsoft.com>
Reviewed-by: Beau Belgrave <beaub@linux.microsoft.com>

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index ad9d6347b5fa03760b32dd1ff61a4dd4972d2dbd..fd1b108ab639e70445ec763760842e28245b3db1 100644 (file)
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -106,13 +106,14 @@ static struct tracepoint_user *__tracepoint_user_init(const char *name, struct t
        if (!tuser->name)
                return NULL;
 
+       /* Register tracepoint if it is loaded. */
        if (tpoint) {
+               tuser->tpoint = tpoint;
                ret = tracepoint_user_register(tuser);
                if (ret)
                        return ERR_PTR(ret);
        }
 
-       tuser->tpoint = tpoint;
        tuser->refcount = 1;
        INIT_LIST_HEAD(&tuser->list);
        list_add(&tuser->list, &tracepoint_user_list);