sunrpc: fix cache_head leak due to queued request

After commit d202cce896, an expired cache_head can be removed from the
cache_detail's hash.

However, the expired cache_head may be waiting for a reply from a
previously submitted request. Such a cache_head has an increased
refcounter and therefore it won't be freed after cache_put(freeme).

Because the cache_head was removed from the hash it cannot be found
during cache_clean() and can be leaked forever, together with stalled
cache_request and other taken resources.

In our case we noticed it because an entry in the export cache was
holding a reference on a filesystem.

Fixes d202cce896 ("sunrpc: never return expired entries in sunrpc_cache_lookup")
Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: stable@kernel.org # 2.6.35
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Reviewed-by: NeilBrown <neilb@suse.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/cache.c

@@ -54,6 +54,11 @@ static void cache_init(struct cache_head *h, struct cache_detail *detail)
 	h->last_refresh = now;
 }
 
+static void cache_fresh_locked(struct cache_head *head, time_t expiry,
+				struct cache_detail *detail);
+static void cache_fresh_unlocked(struct cache_head *head,
+				struct cache_detail *detail);
+
 static struct cache_head *sunrpc_cache_find_rcu(struct cache_detail *detail,
 						struct cache_head *key,
 						int hash)
@@ -100,6 +105,7 @@ static struct cache_head *sunrpc_cache_add_entry(struct cache_detail *detail,
 			if (cache_is_expired(detail, tmp)) {
 				hlist_del_init_rcu(&tmp->cache_list);
 				detail->entries --;
+				cache_fresh_locked(tmp, 0, detail);
 				freeme = tmp;
 				break;
 			}
@@ -115,8 +121,10 @@ static struct cache_head *sunrpc_cache_add_entry(struct cache_detail *detail,
 	cache_get(new);
 	spin_unlock(&detail->hash_lock);
 
-	if (freeme)
+	if (freeme) {
+		cache_fresh_unlocked(freeme, detail);
 		cache_put(freeme, detail);
+	}
 	return new;
 }