handle_async_copy calling kzalloc under spinlock

[bfields@fieldses.org (J. Bruce Fields)]

From bc0c9079b48d "NFS handle COPY reply CB_OFFLOAD call race":

+       spin_lock(&server->nfs_client->cl_lock);
+       list_for_each_entry(copy, &server->nfs_client->pending_cb_stateids,
+                               copies) {
+               if (memcmp(&res->write_res.stateid, &copy->stateid,
+                               NFS4_STATEID_SIZE))
+                       continue;
+               found_pending = true;
+               list_del(&copy->copies);
+               break;
+       }
+       if (found_pending) {
+               spin_unlock(&server->nfs_client->cl_lock);
+               goto out;
+       }
 
        copy = kzalloc(sizeof(struct nfs4_copy_state), GFP_NOFS);

At this point we're still holding cl_lock.

Best might be to allocate "copy" before taking the lock, then free it on any
paths where we don't end up needing it.

--b.