linux-ext4 - [PATCH 12/20] cache: add a helper to grab a new refcount for a cache

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Message-ID: <175573713023.20753.17208085171701652235.stgit@frogsfrogsfrogs>
Date: Wed, 20 Aug 2025 18:11:00 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: tytso@....edu
Cc: John@...ves.net, bernd@...ernd.com, linux-fsdevel@...r.kernel.org,
 linux-ext4@...r.kernel.org, miklos@...redi.hu, amir73il@...il.com,
 joannelkoong@...il.com, neal@...pa.dev
Subject: [PATCH 12/20] cache: add a helper to grab a new refcount for a
 cache_node

From: Darrick J. Wong <djwong@...nel.org>

Create a helper to bump the refcount of a cache node.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 lib/support/cache.h |    1 +
 lib/support/cache.c |   57 +++++++++++++++++++++++++++++----------------------
 2 files changed, 33 insertions(+), 25 deletions(-)


diff --git a/lib/support/cache.h b/lib/support/cache.h
index b18b6d3325e9ad..e8f1c82ef7869c 100644
--- a/lib/support/cache.h
+++ b/lib/support/cache.h
@@ -141,5 +141,6 @@ int cache_node_get_priority(struct cache_node *);
 int cache_node_purge(struct cache *, cache_key_t, struct cache_node *);
 void cache_report(FILE *fp, const char *, struct cache *);
 int cache_overflowed(struct cache *);
+struct cache_node *cache_node_grab(struct cache *cache, struct cache_node *node);
 
 #endif	/* __CACHE_H__ */
diff --git a/lib/support/cache.c b/lib/support/cache.c
index 606acd5453cf10..49568ffa6de2e4 100644
--- a/lib/support/cache.c
+++ b/lib/support/cache.c
@@ -362,6 +362,35 @@ __cache_node_purge(
 	return 0;
 }
 
+/* Grab a new refcount to the cache node object.  Caller must hold cn_mutex. */
+struct cache_node *cache_node_grab(struct cache *cache, struct cache_node *node)
+{
+	struct cache_mru *mru;
+
+	if (node->cn_count == 0 && cache->get) {
+		int err = cache->get(cache, node);
+		if (err)
+			return NULL;
+	}
+	if (node->cn_count == 0) {
+		ASSERT(node->cn_priority >= 0);
+		ASSERT(!list_empty(&node->cn_mru));
+		mru = &cache->c_mrus[node->cn_priority];
+		pthread_mutex_lock(&mru->cm_mutex);
+		mru->cm_count--;
+		list_del_init(&node->cn_mru);
+		pthread_mutex_unlock(&mru->cm_mutex);
+		if (node->cn_old_priority != -1) {
+			ASSERT(node->cn_priority ==
+					CACHE_DIRTY_PRIORITY);
+			node->cn_priority = node->cn_old_priority;
+			node->cn_old_priority = -1;
+		}
+	}
+	node->cn_count++;
+	return node;
+}
+
 /*
  * Lookup in the cache hash table.  With any luck we'll get a cache
  * hit, in which case this will all be over quickly and painlessly.
@@ -377,7 +406,6 @@ cache_node_get(
 	struct cache_node	**nodep)
 {
 	struct cache_hash	*hash;
-	struct cache_mru	*mru;
 	struct cache_node	*node = NULL, *n;
 	unsigned int		hashidx;
 	int			priority = 0;
@@ -411,31 +439,10 @@ cache_node_get(
 			 * from its MRU list, and update stats.
 			 */
 			pthread_mutex_lock(&node->cn_mutex);
-
-			if (node->cn_count == 0 && cache->get) {
-				int err = cache->get(cache, node);
-				if (err) {
-					pthread_mutex_unlock(&node->cn_mutex);
-					goto next_object;
-				}
+			if (!cache_node_grab(cache, node)) {
+				pthread_mutex_unlock(&node->cn_mutex);
+				goto next_object;
 			}
-			if (node->cn_count == 0) {
-				ASSERT(node->cn_priority >= 0);
-				ASSERT(!list_empty(&node->cn_mru));
-				mru = &cache->c_mrus[node->cn_priority];
-				pthread_mutex_lock(&mru->cm_mutex);
-				mru->cm_count--;
-				list_del_init(&node->cn_mru);
-				pthread_mutex_unlock(&mru->cm_mutex);
-				if (node->cn_old_priority != -1) {
-					ASSERT(node->cn_priority ==
-							CACHE_DIRTY_PRIORITY);
-					node->cn_priority = node->cn_old_priority;
-					node->cn_old_priority = -1;
-				}
-			}
-			node->cn_count++;
-
 			pthread_mutex_unlock(&node->cn_mutex);
 			pthread_mutex_unlock(&hash->ch_mutex);