linux-kernel - [PATCH 1/2] dm pcache: fix cache info indexing

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Message-ID: <20251202121158.111092-2-me@linux.beauty>
Date: Tue,  2 Dec 2025 20:11:57 +0800
From: Li Chen <me@...ux.beauty>
To: dm-devel@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Dongsheng Yang <dongsheng.yang@...ux.dev>,
	Zheng Gu <cengku@...il.com>
Subject: [PATCH 1/2] dm pcache: fix cache info indexing

From: Li Chen <chenl311@...natelecom.cn>

The on-media cache_info index used sizeof(struct) instead of the
4K metadata stride, so gc_percent updates from dmsetup message
were written between slots and lost after reboot. Use
PCACHE_CACHE_INFO_SIZE in get_cache_info_addr() and align
info_index with the slot returned by pcache_meta_find_latest().

Signed-off-by: Li Chen <chenl311@...natelecom.cn>
---
 drivers/md/dm-pcache/cache.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
index 698697a7a73c..6d5001548628 100644
--- a/drivers/md/dm-pcache/cache.c
+++ b/drivers/md/dm-pcache/cache.c
@@ -8,9 +8,11 @@
 
 struct kmem_cache *key_cache;
 
-static inline struct pcache_cache_info *get_cache_info_addr(struct pcache_cache *cache)
+static inline struct pcache_cache_info *
+get_cache_info_addr(struct pcache_cache *cache)
 {
-	return cache->cache_info_addr + cache->info_index;
+	return (struct pcache_cache_info *)((char *)cache->cache_info_addr +
+						(size_t)cache->info_index * PCACHE_CACHE_INFO_SIZE);
 }
 
 static void cache_info_write(struct pcache_cache *cache)
@@ -40,7 +42,12 @@ static int cache_info_init(struct pcache_cache *cache, struct pcache_cache_optio
 	if (IS_ERR(cache_info_addr))
 		return PTR_ERR(cache_info_addr);
 
-	if (cache_info_addr) {
+    if (cache_info_addr) {
+		int index = ((char *)cache_info_addr - (char *)cache->cache_info_addr) /
+				PCACHE_CACHE_INFO_SIZE;
+
+		cache->info_index = (index + 1) % PCACHE_META_INDEX_MAX;
+
 		if (opts->data_crc !=
 				(cache->cache_info.flags & PCACHE_CACHE_FLAGS_DATA_CRC)) {
 			pcache_dev_err(pcache, "invalid option for data_crc: %s, expected: %s",
-- 
2.51.0