[bug report] staging: erofs: tidy up decompression frontend

[Dan Carpenter]

Hello Gao Xiang,

The patch 97e86a858bc3: "staging: erofs: tidy up decompression
frontend" from Jul 31, 2019, leads to the following static checker
warning:

	fs/erofs/zdata.c:443 z_erofs_register_collection()
	error: double unlocked 'cl->lock' (orig line 439)

fs/erofs/zdata.c
   432          cl = z_erofs_primarycollection(pcl);
   433          cl->pageofs = map->m_la & ~PAGE_MASK;
   434  
   435          /*
   436           * lock all primary followed works before visible to others
   437           * and mutex_trylock *never* fails for a new pcluster.
   438           */
   439          mutex_trylock(&cl->lock);
                ^^^^^^^^^^^^^^^^^^^^^^^^
   440  
   441          err = erofs_register_workgroup(inode->i_sb, &pcl->obj, 0);
   442          if (err) {
   443                  mutex_unlock(&cl->lock);
                        ^^^^^^^^^^^^^^^^^^^^^^^
How can we unlock if we don't know that the trylock succeeded?

   444                  kmem_cache_free(pcluster_cachep, pcl);
   445                  return -EAGAIN;
   446          }
   447          /* used to check tail merging loop due to corrupted images */
   448          if (clt->owned_head == Z_EROFS_PCLUSTER_TAIL)
   449                  clt->tailpcl = pcl;
   450          clt->owned_head = &pcl->next;
   451          clt->pcl = pcl;
   452          clt->cl = cl;
   453          return 0;

regards,
dan carpenter