[PATCH perf/core 01/11] uprobes: Add unique flag to uprobe consumer

[Jiri Olsa <jolsa@kernel.org>]

Adding unique flag to uprobe consumer to ensure it's the only consumer
attached on the uprobe.

This is helpful for use cases when consumer wants to change user space
registers, which might confuse other consumers. With this change we can
ensure there's only one consumer on specific uprobe.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 include/linux/uprobes.h |  1 +
 kernel/events/uprobes.c | 30 ++++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index 08ef78439d0d..0df849dee720 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -60,6 +60,7 @@ struct uprobe_consumer {
 	struct list_head cons_node;
 
 	__u64 id;	/* set when uprobe_consumer is registered */
+	bool is_unique; /* the only consumer on uprobe */
 };
 
 #ifdef CONFIG_UPROBES
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 996a81080d56..b9b088f7333a 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1024,14 +1024,35 @@ static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
 	return uprobe;
 }
 
-static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
+static bool consumer_can_add(struct list_head *head, struct uprobe_consumer *uc)
+{
+	/* Uprobe has no consumer, we can add any. */
+	if (list_empty(head))
+		return true;
+	/* Uprobe has consumer/s, we can't add unique one. */
+	if (uc->is_unique)
+		return false;
+	/*
+	 * Uprobe has consumer/s, we can add nother consumer only if the
+	 * current consumer is not unique.
+	 **/
+	return !list_first_entry(head, struct uprobe_consumer, cons_node)->is_unique;
+}
+
+static int consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
 {
 	static atomic64_t id;
+	int ret = -EBUSY;
 
 	down_write(&uprobe->consumer_rwsem);
+	if (!consumer_can_add(&uprobe->consumers, uc))
+		goto unlock;
 	list_add_rcu(&uc->cons_node, &uprobe->consumers);
 	uc->id = (__u64) atomic64_inc_return(&id);
+	ret = 0;
+unlock:
 	up_write(&uprobe->consumer_rwsem);
+	return ret;
 }
 
 /*
@@ -1420,7 +1441,12 @@ struct uprobe *uprobe_register(struct inode *inode,
 		return uprobe;
 
 	down_write(&uprobe->register_rwsem);
-	consumer_add(uprobe, uc);
+	ret = consumer_add(uprobe, uc);
+	if (ret) {
+		put_uprobe(uprobe);
+		up_write(&uprobe->register_rwsem);
+		return ERR_PTR(ret);
+	}
 	ret = register_for_each_vma(uprobe, uc);
 	up_write(&uprobe->register_rwsem);
 
-- 
2.51.0