0001-task_finder_vma-add-kfree_rcu-compat-for-old-unpatch.patch

From 5bc135475f0573d4651e96ee9786d29e685b3774 Mon Sep 17 00:00:00 2001
From: Sultan Alsawaf <sultan@openresty.com>
Date: Tue, 1 Dec 2020 10:06:50 -0800
Subject: [PATCH] task_finder_vma: add kfree_rcu() compat for old unpatched
 kernels

Newer RHEL 6 kernels have kfree_rcu(), but older ones do not. Using
kfree_rcu() is beneficial because it lets the RCU subsystem know that
the queued RCU callback is low-priority, and can be deferred, hence why
we don't replace kfree_rcu() with call_rcu() outright.
---
 runtime/task_finder_vma.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/runtime/task_finder_vma.c b/runtime/task_finder_vma.c
index 7f0f6ed56..831ad6932 100644
--- a/runtime/task_finder_vma.c
+++ b/runtime/task_finder_vma.c
@@ -87,6 +87,15 @@ __stp_tf_vma_new_entry(void)
 	return entry;
 }
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3,0,0)
+static void __stp_tf_vma_free_entry(struct rcu_head *rcu)
+{
+	struct __stp_tf_vma_entry *entry = container_of(rcu, typeof(*entry), rcu);
+
+	kfree(entry);
+}
+#endif
+
 // __stp_tf_vma_put_entry(): Put a specified number of references on the entry.
 static void
 __stp_tf_vma_put_entry(struct __stp_tf_vma_bucket *bucket,
@@ -106,7 +115,11 @@ __stp_tf_vma_put_entry(struct __stp_tf_vma_bucket *bucket,
 	hlist_del_rcu(&entry->hlist);
 	stp_spin_unlock_irqrestore(&bucket->lock, flags);
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(3,0,0)
+	call_rcu(&entry->rcu, __stp_tf_vma_free_entry);
+#else
 	kfree_rcu(entry, rcu);
+#endif
 }
 
 // stap_initialize_vma_map():  Initialize the free list.  Grabs the
-- 
2.29.2