[PATCH 02/12] tracing/probes: Enable newly appended probe when target event is enabled

["Masami Hiramatsu (Google)" <mhiramat@kernel.org>]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Unlike kprobe events, fprobe and uprobe events only register their
underlying probes when the trace event is enabled. When a new probe is
appended to an existing multiprobe fprobe or uprobe event that is
already enabled, the appended probe is linked into the event's probe
list without being registered.

As a result, the newly appended probe never fires until the event is
disabled and re-enabled. Moreover, disabling an fprobe event calls
unregister_fprobe() on the unregistered fprobe, and opening or closing a
perf event on an enabled uprobe event dereferences a NULL tu->uprobe in
uprobe_apply().

Register and enable the newly appended fprobe or uprobe immediately when
the target event is already enabled.

Fixes: 41af3cf587f4 ("tracing/uprobe: Add multi-probe per uprobe event support")
Fixes: 2db832ec9090 ("tracing: fprobe-events: Register fprobe-events only when it is enabled")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 kernel/trace/trace_fprobe.c |   14 +++++------
 kernel/trace/trace_uprobe.c |   56 ++++++++++++++++++++++++++++---------------
 2 files changed, 43 insertions(+), 27 deletions(-)

diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
index 77f2228d44ba..9ab0871a6461 100644
--- a/kernel/trace/trace_fprobe.c
+++ b/kernel/trace/trace_fprobe.c
@@ -933,7 +933,10 @@ static int append_trace_fprobe_event(struct trace_fprobe *tf, struct trace_fprob
 	if (ret)
 		return ret;
 
-	ret = trace_fprobe_verify_target(tf);
+	if (trace_probe_is_enabled(&tf->tp))
+		ret = __register_trace_fprobe(tf);
+	else
+		ret = trace_fprobe_verify_target(tf);
 	if (ret)
 		trace_probe_unlink(&tf->tp);
 	else
@@ -1520,13 +1523,8 @@ static int disable_trace_fprobe(struct trace_event_call *call,
 		trace_probe_clear_flag(tp, TP_FLAG_PROFILE);
 
 	if (!trace_probe_is_enabled(tp)) {
-		list_for_each_entry(tf, trace_probe_probe_list(tp), tp.list) {
-			unregister_fprobe(&tf->fp);
-			if (tf->tuser) {
-				tracepoint_user_put(tf->tuser);
-				tf->tuser = NULL;
-			}
-		}
+		list_for_each_entry(tf, trace_probe_probe_list(tp), tp.list)
+			__unregister_trace_fprobe(tf);
 	}
 
  out:
diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 146da04b93a8..14ac52aebe34 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -447,6 +447,28 @@ static bool trace_uprobe_has_same_uprobe(struct trace_uprobe *orig,
 	return false;
 }
 
+typedef bool (*filter_func_t)(struct uprobe_consumer *self, struct mm_struct *mm);
+
+#ifdef CONFIG_PERF_EVENTS
+static bool uprobe_perf_filter(struct uprobe_consumer *uc, struct mm_struct *mm);
+#else
+#define uprobe_perf_filter NULL
+#endif
+
+static int trace_uprobe_enable(struct trace_uprobe *tu, filter_func_t filter)
+{
+	struct inode *inode = d_real_inode(tu->path.dentry);
+	struct uprobe *uprobe;
+
+	tu->consumer.filter = filter;
+	uprobe = uprobe_register(inode, tu->offset, tu->ref_ctr_offset, &tu->consumer);
+	if (IS_ERR(uprobe))
+		return PTR_ERR(uprobe);
+
+	tu->uprobe = uprobe;
+	return 0;
+}
+
 static int append_trace_uprobe(struct trace_uprobe *tu, struct trace_uprobe *to)
 {
 	int ret;
@@ -466,10 +488,22 @@ static int append_trace_uprobe(struct trace_uprobe *tu, struct trace_uprobe *to)
 
 	/* Append to existing event */
 	ret = trace_probe_append(&tu->tp, &to->tp);
-	if (!ret)
-		dyn_event_add(&tu->devent, trace_probe_event_call(&tu->tp));
+	if (ret)
+		return ret;
 
-	return ret;
+	if (trace_probe_is_enabled(&tu->tp)) {
+		ret = trace_uprobe_enable(tu,
+			trace_probe_test_flag(&tu->tp, TP_FLAG_PROFILE) ?
+			uprobe_perf_filter : NULL);
+		if (ret) {
+			trace_probe_unlink(&tu->tp);
+			return ret;
+		}
+	}
+
+	dyn_event_add(&tu->devent, trace_probe_event_call(&tu->tp));
+
+	return 0;
 }
 
 /*
@@ -1105,22 +1139,6 @@ print_uprobe_event(struct trace_iterator *iter, int flags, struct trace_event *e
 	return trace_handle_return(s);
 }
 
-typedef bool (*filter_func_t)(struct uprobe_consumer *self, struct mm_struct *mm);
-
-static int trace_uprobe_enable(struct trace_uprobe *tu, filter_func_t filter)
-{
-	struct inode *inode = d_real_inode(tu->path.dentry);
-	struct uprobe *uprobe;
-
-	tu->consumer.filter = filter;
-	uprobe = uprobe_register(inode, tu->offset, tu->ref_ctr_offset, &tu->consumer);
-	if (IS_ERR(uprobe))
-		return PTR_ERR(uprobe);
-
-	tu->uprobe = uprobe;
-	return 0;
-}
-
 static void __probe_event_disable(struct trace_probe *tp)
 {
 	struct trace_uprobe *tu;