[RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe event files are open

[Steven Rostedt]

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

When one of the event files is opened, we need to prevent them from
being removed. Modules do with with the module owner set (automated
from the VFS layer).  The ftrace buffer instances have a ref count added
to the trace_array when the enabled file is opened (the others are not
that big of a deal, as they only reference the event calls which
still exist when an instance disappears). But kprobes and uprobes
do not have any protection.

Have the unregister probe fail when the event files are open, in use
are used by perf.

Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace_uprobe.c |   48 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index d5d0cd3..4916da5 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -70,7 +70,7 @@ struct trace_uprobe {
 	(sizeof(struct probe_arg) * (n)))
 
 static int register_uprobe_event(struct trace_uprobe *tu);
-static void unregister_uprobe_event(struct trace_uprobe *tu);
+static int unregister_uprobe_event(struct trace_uprobe *tu);
 
 static DEFINE_MUTEX(uprobe_lock);
 static LIST_HEAD(uprobe_list);
@@ -164,11 +164,17 @@ static struct trace_uprobe *find_probe_event(const char *event, const char *grou
 }
 
 /* Unregister a trace_uprobe and probe_event: call with locking uprobe_lock */
-static void unregister_trace_uprobe(struct trace_uprobe *tu)
+static int unregister_trace_uprobe(struct trace_uprobe *tu)
 {
+	int ret;
+
+	ret = unregister_uprobe_event(tu);
+	if (ret)
+		return ret;
+
 	list_del(&tu->list);
-	unregister_uprobe_event(tu);
 	free_trace_uprobe(tu);
+	return 0;
 }
 
 /* Register a trace_uprobe and probe_event */
@@ -181,9 +187,12 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
 
 	/* register as an event */
 	old_tp = find_probe_event(tu->call.name, tu->call.class->system);
-	if (old_tp)
+	if (old_tp) {
 		/* delete old event */
-		unregister_trace_uprobe(old_tp);
+		ret = unregister_trace_uprobe(old_tp);
+		if (ret)
+			goto end;
+	}
 
 	ret = register_uprobe_event(tu);
 	if (ret) {
@@ -256,6 +265,8 @@ static int create_trace_uprobe(int argc, char **argv)
 		group = UPROBE_EVENT_SYSTEM;
 
 	if (is_delete) {
+		int ret;
+
 		if (!event) {
 			pr_info("Delete command needs an event name.\n");
 			return -EINVAL;
@@ -269,9 +280,9 @@ static int create_trace_uprobe(int argc, char **argv)
 			return -ENOENT;
 		}
 		/* delete an event */
-		unregister_trace_uprobe(tu);
+		ret = unregister_trace_uprobe(tu);
 		mutex_unlock(&uprobe_lock);
-		return 0;
+		return ret;
 	}
 
 	if (argc < 2) {
@@ -408,16 +419,20 @@ fail_address_parse:
 	return ret;
 }
 
-static void cleanup_all_probes(void)
+static int cleanup_all_probes(void)
 {
 	struct trace_uprobe *tu;
+	int ret = 0;
 
 	mutex_lock(&uprobe_lock);
 	while (!list_empty(&uprobe_list)) {
 		tu = list_entry(uprobe_list.next, struct trace_uprobe, list);
-		unregister_trace_uprobe(tu);
+		ret = unregister_trace_uprobe(tu);
+		if (ret)
+			break;
 	}
 	mutex_unlock(&uprobe_lock);
+	return ret;
 }
 
 /* Probes listing interfaces */
@@ -462,8 +477,12 @@ static const struct seq_operations probes_seq_op = {
 
 static int probes_open(struct inode *inode, struct file *file)
 {
+	int ret = 0;
+
 	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC))
-		cleanup_all_probes();
+		ret = cleanup_all_probes();
+	if (ret)
+		return ret;
 
 	return seq_open(file, &probes_seq_op);
 }
@@ -970,12 +989,17 @@ static int register_uprobe_event(struct trace_uprobe *tu)
 	return ret;
 }
 
-static void unregister_uprobe_event(struct trace_uprobe *tu)
+static int unregister_uprobe_event(struct trace_uprobe *tu)
 {
+	int ret;
+
 	/* tu->event is unregistered in trace_remove_event_call() */
-	trace_remove_event_call(&tu->call);
+	ret = trace_remove_event_call(&tu->call);
+	if (ret)
+		return ret;
 	kfree(tu->call.print_fmt);
 	tu->call.print_fmt = NULL;
+	return 0;
 }
 
 /* Make a trace interface for controling probe points */
-- 
1.7.10.4


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