dm cache: fix resize crash if user doesn't reload cache table

snitm · snitm · commit 5d07384a666d · 2018-10-04T15:20:52.000-04:00
A reload of the cache's DM table is needed during resize because otherwise a crash will occur when attempting to access smq policy entries associated with the portion of the cache that was recently extended. The reason is cache-size based data structures in the policy will not be resized, the only way to safely extend the cache is to allow for a proper cache policy initialization that occurs when the cache table is loaded. For example the smq policy's space_init(), init_allocator(), calc_hotspot_params() must be sized based on the extended cache size. The fix for this is to disallow cache resizes of this pattern: 1) suspend "cache" target's device 2) resize the fast device used for the cache 3) resume "cache" target's device Instead, the last step must be a full reload of the cache's DM table. Fixes: 66a6363 ("dm cache: add stochastic-multi-queue (smq) policy") Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
@@ -3009,8 +3009,13 @@ static dm_cblock_t get_cache_dev_size(struct cache *cache)
 
 static bool can_resize(struct cache *cache, dm_cblock_t new_size)
 {
-	if (from_cblock(new_size) > from_cblock(cache->cache_size))
-		return true;
+	if (from_cblock(new_size) > from_cblock(cache->cache_size)) {
+		if (cache->sized) {
+			DMERR("%s: unable to extend cache due to missing cache table reload",
+			      cache_device_name(cache));
+			return false;
+		}
+	}
 
 	/*
 	 * We can't drop a dirty block when shrinking the cache.
