Merge: fprobe: Release rethook after the ftrace_ops is unregistered

MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-9/-/merge_requests/1357

JIRA: https://issues.redhat.com/browse/RHEL-26131

There is a known bug in the fprobe subsystem which may cause a fault while running bpf selftests. This MR backports the upstream commits fixing the issue.

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Approved-by: Jerome Marchand <jmarchan@redhat.com>
Approved-by: John B. Wyatt IV <jwyatt@redhat.com>

Merged-by: Scott Weaver <scweaver@redhat.com>

Author: swvrrh

include/linux/rethook.h

@@ -59,6 +59,7 @@ struct rethook_node {
 };
 
 struct rethook *rethook_alloc(void *data, rethook_handler_t handler);
+void rethook_stop(struct rethook *rh);
 void rethook_free(struct rethook *rh);
 void rethook_add_node(struct rethook *rh, struct rethook_node *node);
 struct rethook_node *rethook_try_get(struct rethook *rh);

kernel/trace/fprobe.c

@@ -349,19 +349,16 @@ int unregister_fprobe(struct fprobe *fp)
 		    fp->ops.saved_func != fprobe_kprobe_handler))
 		return -EINVAL;
 
-	/*
-	 * rethook_free() starts disabling the rethook, but the rethook handlers
-	 * may be running on other processors at this point. To make sure that all
-	 * current running handlers are finished, call unregister_ftrace_function()
-	 * after this.
-	 */
 	if (fp->rethook)
-		rethook_free(fp->rethook);
+		rethook_stop(fp->rethook);
 
 	ret = unregister_ftrace_function(&fp->ops);
 	if (ret < 0)
 		return ret;
 
+	if (fp->rethook)
+		rethook_free(fp->rethook);
+
 	ftrace_free_filter(&fp->ops);
 
 	return ret;

kernel/trace/rethook.c

@@ -53,6 +53,19 @@ static void rethook_free_rcu(struct rcu_head *head)
 		kfree(rh);
 }
 
+/**
+ * rethook_stop() - Stop using a rethook.
+ * @rh: the struct rethook to stop.
+ *
+ * Stop using a rethook to prepare for freeing it. If you want to wait for
+ * all running rethook handler before calling rethook_free(), you need to
+ * call this first and wait RCU, and call rethook_free().
+ */
+void rethook_stop(struct rethook *rh)
+{
+	WRITE_ONCE(rh->handler, NULL);
+}
+
 /**
  * rethook_free() - Free struct rethook.
  * @rh: the struct rethook to be freed.