[PATCH 2/2] dm pcache: fix segment info indexing

[Li Chen <me@linux.beauty>]

From: Li Chen <chenl311@chinatelecom.cn>

Segment info indexing also used sizeof(struct) instead of the
4K metadata stride, so info_index could point between slots and
subsequent writes would advance incorrectly. Derive info_index
from the pointer returned by the segment meta search using
PCACHE_SEG_INFO_SIZE and advance to the next slot for future
updates.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
---
 drivers/md/dm-pcache/cache_segment.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-pcache/cache_segment.c b/drivers/md/dm-pcache/cache_segment.c
index f0b58980806e..0b4bb08011ce 100644
--- a/drivers/md/dm-pcache/cache_segment.c
+++ b/drivers/md/dm-pcache/cache_segment.c
@@ -56,7 +56,11 @@ static int cache_seg_info_load(struct pcache_cache_segment *cache_seg)
 		ret = -EIO;
 		goto out;
 	}
-	cache_seg->info_index = cache_seg_info_addr - cache_seg_info_addr_base;
+
+	cache_seg->info_index =
+		((char *)cache_seg_info_addr - (char *)cache_seg_info_addr_base) /
+		PCACHE_SEG_INFO_SIZE;
+	cache_seg->info_index = (cache_seg->info_index + 1) % PCACHE_META_INDEX_MAX;
 out:
 	mutex_unlock(&cache_seg->info_lock);
 
-- 
2.51.0