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

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: d4b7d8826 ("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
index a534133717254a88eb91e025c7731e408fbbdfad..e13d991e9fb52eff6176e2a275c8a8d2342b6701 100644 (file)
--- 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.