在 12/5/2025 12:13 AM, Mikulas Patocka 写道:
On Thu, 4 Dec 2025, Dongsheng Yang wrote:
In dm-pcache, in order to ensure crash-consistency, a dual-copy scheme
is used to alternately update metadata, and there is a slot index that
records the current slot. However, in the write path the current
implementation writes directly to the current slot indexed by slot
index, and then advances the slot — which ends up overwriting the
existing slot, violating the crash-consistency guarantee.
This patch fixes that behavior, preventing metadata from being
overwritten incorrectly.
Signed-off-by: Dongsheng Yang <[email protected]>
---
drivers/md/dm-pcache/cache.c | 8 ++++----
drivers/md/dm-pcache/cache_segment.c | 8 ++++----
2 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/drivers/md/dm-pcache/cache.c b/drivers/md/dm-pcache/cache.c
index 698697a7a73c..9289c016b7c9 100644
--- a/drivers/md/dm-pcache/cache.c
+++ b/drivers/md/dm-pcache/cache.c
@@ -21,10 +21,10 @@ static void cache_info_write(struct pcache_cache *cache)
cache_info->header.crc = pcache_meta_crc(&cache_info->header,
sizeof(struct
pcache_cache_info));
+ cache->info_index = (cache->info_index + 1) % PCACHE_META_INDEX_MAX;
+
memcpy_flushcache(get_cache_info_addr(cache), cache_info,
sizeof(struct pcache_cache_info));
-
- cache->info_index = (cache->info_index + 1) % PCACHE_META_INDEX_MAX;
}
static void cache_info_init_default(struct pcache_cache *cache);
I'm not sure whether this is bug or not
It's a bug, if in-place updating for slot happen, there is a potential
metadata corruption while powercut happening at the same time.
so I will add
Cc: [email protected] # 6.18
in V2.
- but memcpy_flushcache doesn't
guarantee that the cache will be flushed (despite it's name) or that
writes would be ordered.
You need pmem_wmb(). I see that you are using it at other places.
Good catch, I will send v2 to add the missing pmem_wmb().
Thanx
Mikulas
