linux-hardening - [RFC PATCH v2 01/19] list: Support getting most recent element in list

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Message-Id: <20210830235927.6443-2-rick.p.edgecombe@intel.com>
Date:   Mon, 30 Aug 2021 16:59:09 -0700
From:   Rick Edgecombe <rick.p.edgecombe@...el.com>
To:     dave.hansen@...el.com, luto@...nel.org, peterz@...radead.org,
        x86@...nel.org, akpm@...ux-foundation.org, keescook@...omium.org,
        shakeelb@...gle.com, vbabka@...e.cz, rppt@...nel.org
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>, linux-mm@...ck.org,
        linux-hardening@...r.kernel.org,
        kernel-hardening@...ts.openwall.com, ira.weiny@...el.com,
        dan.j.williams@...el.com, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v2 01/19] list: Support getting most recent element in list_lru

In future patches, some functionality will use list_lru that also needs
to keep track of the most recently used element on a node. Since this
information is already contained within list_lru, add a function to get
it so that an additional list is not needed in the caller.

Do not support memcg aware list_lru's since it is not needed by the
intended caller.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
---
 include/linux/list_lru.h | 13 +++++++++++++
 mm/list_lru.c            | 28 ++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/include/linux/list_lru.h b/include/linux/list_lru.h
index 1b5fceb565df..08e07c19fd13 100644
--- a/include/linux/list_lru.h
+++ b/include/linux/list_lru.h
@@ -103,6 +103,19 @@ bool list_lru_add(struct list_lru *lru, struct list_head *item);
  */
 bool list_lru_del(struct list_lru *lru, struct list_head *item);
 
+/**
+ * list_lru_get_mru: gets and removes the tail from one of the node lists
+ * @list_lru: the lru pointer
+ * @nid: the node id
+ *
+ * This function removes the most recently added item from one of the node
+ * id specified. This function should not be used if the list_lru is memcg
+ * aware.
+ *
+ * Return value: The element removed
+ */
+struct list_head *list_lru_get_mru(struct list_lru *lru, int nid);
+
 /**
  * list_lru_count_one: return the number of objects currently held by @lru
  * @lru: the lru pointer.
diff --git a/mm/list_lru.c b/mm/list_lru.c
index cd58790d0fb3..c1bec58168e1 100644
--- a/mm/list_lru.c
+++ b/mm/list_lru.c
@@ -156,6 +156,34 @@ bool list_lru_del(struct list_lru *lru, struct list_head *item)
 }
 EXPORT_SYMBOL_GPL(list_lru_del);
 
+struct list_head *list_lru_get_mru(struct list_lru *lru, int nid)
+{
+	struct list_lru_node *nlru = &lru->node[nid];
+	struct list_lru_one *l = &nlru->lru;
+	struct list_head *ret;
+
+	/* This function does not attempt to search through the memcg lists */
+	if (list_lru_memcg_aware(lru)) {
+		WARN_ONCE(1, "list_lru: %s not supported on memcg aware list_lrus", __func__);
+		return NULL;
+	}
+
+	spin_lock(&nlru->lock);
+	if (list_empty(&l->list)) {
+		ret = NULL;
+	} else {
+		/* Get tail */
+		ret = l->list.prev;
+		list_del_init(ret);
+
+		l->nr_items--;
+		nlru->nr_items--;
+	}
+	spin_unlock(&nlru->lock);
+
+	return ret;
+}
+
 void list_lru_isolate(struct list_lru_one *list, struct list_head *item)
 {
 	list_del_init(item);
-- 
2.17.1