[bug report] bcache: explicitly make cache_set only have single cache

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Coly Li,

This is a semi-automatic email about new static checker warnings.

The patch 697e23495c94: "bcache: explicitly make cache_set only have 
single cache" from Oct 1, 2020, leads to the following Smatch 
complaint:

    drivers/md/bcache/super.c:2157 register_cache_set()
    error: we previously assumed 'c->cache' could be null (see line 2125)

drivers/md/bcache/super.c
  2124			if (!memcmp(c->set_uuid, ca->sb.set_uuid, 16)) {
  2125				if (c->cache)
                                    ^^^^^^^^

  2126					return "duplicate cache set member";
  2127	
  2128				goto found;
                                ^^^^^^^^^^
"c->cache" is NULL on this path.

  2129			}
  2130	
  2131		c = bch_cache_set_alloc(&ca->sb);
  2132		if (!c)
  2133			return err;
  2134	
  2135		err = "error creating kobject";
  2136		if (kobject_add(&c->kobj, bcache_kobj, "%pU", c->set_uuid) ||
  2137		    kobject_add(&c->internal, &c->kobj, "internal"))
  2138			goto err;
  2139	
  2140		if (bch_cache_accounting_add_kobjs(&c->accounting, &c->kobj))
  2141			goto err;
  2142	
  2143		bch_debug_init_cache_set(c);
  2144	
  2145		list_add(&c->list, &bch_cache_sets);
  2146	found:
  2147		sprintf(buf, "cache%i", ca->sb.nr_this_dev);
  2148		if (sysfs_create_link(&ca->kobj, &c->kobj, "set") ||
  2149		    sysfs_create_link(&c->kobj, &ca->kobj, buf))
  2150			goto err;
  2151	
  2152		kobject_get(&ca->kobj);
  2153		ca->set = c;
  2154		ca->set->cache = ca;
  2155	
  2156		err = "failed to run cache set";
  2157		if (run_cache_set(c) < 0)
                    ^^^^^^^^^^^^^^^^
c->cache gets dereferenced inside this function without checking when we
do "c->nbuckets = ca->sb.nbuckets;".

  2158			goto err;
  2159	

regards,
dan carpenter