linux-kernel - [RFT PATCH 12/13] tracing/kprobe: Free probe event asynchronously

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Date:   Thu, 16 Jan 2020 23:46:17 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Brendan Gregg <brendan.d.gregg@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     mhiramat@...nel.org, Ingo Molnar <mingo@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "David S . Miller" <davem@...emloft.net>, paulmck@...nel.org,
        joel@...lfernandes.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Subject: [RFT PATCH 12/13] tracing/kprobe: Free probe event asynchronously

Free each probe event data structure asynchronously when
deleting probe events. But this finally synchronizes RCU
so that we make sure all event handlers have finished.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
---
 kernel/trace/trace_dynevent.c |    5 ++++
 kernel/trace/trace_kprobe.c   |   46 +++++++++++++++++++++++++++++++++++------
 2 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace_dynevent.c b/kernel/trace/trace_dynevent.c
index 89779eb84a07..2d5e8d457309 100644
--- a/kernel/trace/trace_dynevent.c
+++ b/kernel/trace/trace_dynevent.c
@@ -70,6 +70,9 @@ int dyn_event_release(int argc, char **argv, struct dyn_event_operations *type)
 		if (ret)
 			break;
 	}
+
+	/* Wait for running events because of async event unregistration */
+	synchronize_rcu();
 	mutex_unlock(&event_mutex);
 
 	return ret;
@@ -164,6 +167,8 @@ int dyn_events_release_all(struct dyn_event_operations *type)
 		if (ret)
 			break;
 	}
+	/* Wait for running events because of async event unregistration */
+	synchronize_rcu();
 out:
 	mutex_unlock(&event_mutex);
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 906af1ffe2b2..f7e0370b10ae 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -551,7 +551,35 @@ static void __unregister_trace_kprobe(struct trace_kprobe *tk)
 	}
 }
 
-/* Unregister a trace_probe and probe_event */
+static void free_trace_kprobe_cb(struct rcu_head *head)
+{
+	struct kprobe *kp = container_of(head, struct kprobe, rcu);
+	struct kretprobe *rp = container_of(kp, struct kretprobe, kp);
+	struct trace_kprobe *tk = container_of(rp, struct trace_kprobe, rp);
+
+	if (trace_kprobe_is_return(tk))
+		kretprobe_free_callback(head);
+	else
+		kprobe_free_callback(head);
+	free_trace_kprobe(tk);
+}
+
+static void __unregister_trace_kprobe_async(struct trace_kprobe *tk)
+{
+	if (trace_kprobe_is_registered(tk)) {
+		if (trace_kprobe_is_return(tk))
+			unregister_kretprobe_async(&tk->rp,
+						   free_trace_kprobe_cb);
+		else
+			unregister_kprobe_async(&tk->rp.kp,
+						free_trace_kprobe_cb);
+	}
+}
+
+/*
+ * Unregister a trace_probe and probe_event asynchronously.
+ * Caller must wait for RCU.
+ */
 static int unregister_trace_kprobe(struct trace_kprobe *tk)
 {
 	/* If other probes are on the event, just unregister kprobe */
@@ -570,9 +598,17 @@ static int unregister_trace_kprobe(struct trace_kprobe *tk)
 		return -EBUSY;
 
 unreg:
-	__unregister_trace_kprobe(tk);
 	dyn_event_remove(&tk->devent);
+	/*
+	 * This trace_probe_unlink() can free the trace_event_call linked to
+	 * this probe.
+	 * We can do this before unregistering because this probe is
+	 * already disabled and the disabling process waits enough period
+	 * for all handlers finished. IOW, the disabling process must wait
+	 * RCU sync at least once before returning to its caller.
+	 */
 	trace_probe_unlink(&tk->tp);
+	__unregister_trace_kprobe_async(tk);
 
 	return 0;
 }
@@ -928,11 +964,7 @@ static int create_or_delete_trace_kprobe(int argc, char **argv)
 static int trace_kprobe_release(struct dyn_event *ev)
 {
 	struct trace_kprobe *tk = to_trace_kprobe(ev);
-	int ret = unregister_trace_kprobe(tk);
-
-	if (!ret)
-		free_trace_kprobe(tk);
-	return ret;
+	return unregister_trace_kprobe(tk);
 }
 
 static int trace_kprobe_show(struct seq_file *m, struct dyn_event *ev)