cifs: Defer read completion

Defer read completion from the I/O thread to the cifsiod thread so as not
to slow down the I/O thread. This restores the behaviour of v6.9.

Fixes: 3ee1a1fc3981 ("cifs: Cut over to using netfslib")
Signed-off-by: David Howells <[e-mail]>
cc: Paulo Alcantara <[e-mail]>
cc: Jeff Layton <[e-mail]>
cc: [e-mail]
cc: [e-mail]
cc: [e-mail]
Signed-off-by: Steve French <[e-mail]>

fs/smb/client/smb2pdu.c

···
 	return rc;
 }
 
+static void smb2_readv_worker(struct work_struct *work)
+{
+	struct cifs_io_subrequest *rdata =
+		container_of(work, struct cifs_io_subrequest, subreq.work);
+
+	netfs_subreq_terminated(&rdata->subreq,
+				(rdata->result == 0 || rdata->result == -EAGAIN) ?
+				rdata->got_bytes : rdata->result, true);
+}
+
 static void
 smb2_readv_callback(struct mid_q_entry *mid)
 {
···
 			rdata->result = 0;
 	}
 	rdata->credits.value = 0;
-	netfs_subreq_terminated(&rdata->subreq,
-				(rdata->result == 0 || rdata->result == -EAGAIN) ?
-				rdata->got_bytes : rdata->result, true);
+	INIT_WORK(&rdata->subreq.work, smb2_readv_worker);
+	queue_work(cifsiod_wq, &rdata->subreq.work);
 	release_mid(mid);
 	add_credits(server, &credits, 0);
 }