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[dm-devel] dm-cache: resize_cache_dev resizing to wrong size ?



Hi.

CC'ing f494a9c6b1b6dd9a9f21bbb75d9210d478eeb498 author.
Please keep me CC'ed in replies, I'm not subscribed.

Wandering aimlessly in dm-cache source as of current linus master
(3.13-rc2, dc1ccc48159d63eca5089e507c82c7d22ef60839), I noticed this:

dm-cache-metadata.c:
  int dm_cache_resize(struct dm_cache_metadata *cmd, dm_cblock_t new_cache_size)

Note second argument is new_cache_size. But caller is doing:

dm-cache-target.c:
  static int resize_cache_dev(struct cache *cache, dm_cblock_t new_size)
  [...]
    r = dm_cache_resize(cache->cmd, cache->cache_size);
  [...]
    cache->cache_size = new_size;

dm_cache_resize is called with cache->cache_size before it gets updated
to new_size, so it looks like a no-op.

Can someone confirm my reading ?

If confirmed, the effect is that a shrink (only ? I'm not familiar with
cache metadata) operation can result in metadata inconsistent with
cache device size.

See attachment for proposed (untested) fix.
It applies cleanly as of current device-mapper for-next branch.

Regards,
-- 
Vincent Pelletier
>From 99fe12976eae6abd67be0c39798c61ca9acd683d Mon Sep 17 00:00:00 2001
Message-Id: <99fe12976eae6abd67be0c39798c61ca9acd683d 1385805937 git plr vincent gmail com>
From: Vincent Pelletier <plr vincent gmail com>
Date: Sat, 30 Nov 2013 11:05:12 +0100
Subject: dm cache: actually shrink cache to new size

Signed-off-by: Vincent Pelletier <plr vincent gmail com>
---
 drivers/md/dm-cache-target.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 9efcf10..1b1469e 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2755,7 +2755,7 @@ static int resize_cache_dev(struct cache *cache, dm_cblock_t new_size)
 {
 	int r;
 
-	r = dm_cache_resize(cache->cmd, cache->cache_size);
+	r = dm_cache_resize(cache->cmd, new_size);
 	if (r) {
 		DMERR("could not resize cache metadata");
 		return r;
-- 
1.8.4.4


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