On Fri, Jul 03, 2026 at 03:27:00PM +0800, Qingfang Deng wrote:

Hi,

On 2026/7/2 2:12, Norbert Szetei wrote:

quoted

+/* Purge after the grace period: a late ppp_input() may still queue an
+ * skb on pch->file.rq before the last RCU reader drains.
+ */
+static void ppp_release_channel_free(struct rcu_head *rcu)
+{
+	struct channel *pch = container_of(rcu, struct channel, rcu);
+
+	skb_queue_purge(&pch->file.xq);
+	skb_queue_purge(&pch->file.rq);
+	kfree(pch);
+}
+
  /*
   * Drop a reference to a ppp channel and free its memory if the refcount reaches
   * zero.

@@ -3581,9 +3594,7 @@ static void ppp_release_channel(struct channel *pch)
  		pr_err("ppp: destroying undead channel %p !\n", pch);
  		return;
  	}
-	skb_queue_purge(&pch->file.xq);
-	skb_queue_purge(&pch->file.rq);
-	kfree(pch);
+	call_rcu(&pch->rcu, ppp_release_channel_free);
  }
  static void __exit ppp_cleanup(void)

AI-review found an issue: https://sashiko.dev/#/patchset/D9C0245B-608B-4884-8A09-F55BA4A9F948%40doyensec.com

An rcu_barrier() call is needed at the end of ppp_cleanup().

I was initially unclear why rcu_barrier() would be necessary on a kfree path,
but it appears to be required during module unload to ensure that
ppp_release_channel_free() completes before the module's struct rcu_head is
destroyed. Is that the correct understanding?