Re: [PATCH v2] tracing/uprobe: Add missing PID filter for uretprobe

On 08/27, Jiri Olsa wrote:

On Tue, Aug 27, 2024 at 12:40:52PM +0200, Oleg Nesterov wrote:

quoted

 static bool
 uprobe_multi_link_filter(struct uprobe_consumer *con, struct mm_struct *mm)
 {
 	struct bpf_uprobe *uprobe;
+	struct task_struct *task, *t;
+	bool ret = false;

 	uprobe = container_of(con, struct bpf_uprobe, consumer);
-	return uprobe->link->task->mm == mm;
+	task = uprobe->link->task;
+
+	rcu_read_lock();
+	for_each_thread(task, t) {
+		struct mm_struct *mm = READ_ONCE(t->mm);
+		if (mm) {
+			ret = t->mm == mm;
+			break;
+		}
+	}
+	rcu_read_unlock();

that seems expensive if there's many threads

many threads with ->mm == NULL? In the likely case for_each_thread()
stops after the first t->mm check.

could we check the leader first and only if it's gone fallback to this?

up to you..

Oleg.