Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751989AbdFUUjq (ORCPT ); Wed, 21 Jun 2017 16:39:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:33916 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751038AbdFUUjp (ORCPT ); Wed, 21 Jun 2017 16:39:45 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D126A217C6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=sstabellini@kernel.org Date: Wed, 21 Jun 2017 13:39:40 -0700 (PDT) From: Stefano Stabellini X-X-Sender: sstabellini@sstabellini-ThinkPad-X260 To: Boris Ostrovsky cc: Stefano Stabellini , xen-devel@lists.xen.org, linux-kernel@vger.kernel.org, jgross@suse.com, Stefano Stabellini Subject: Re: [PATCH v4 12/18] xen/pvcalls: implement poll command In-Reply-To: <15ea89f6-d46e-2495-1b52-d7290b47c478@oracle.com> Message-ID: References: <1497553787-3709-1-git-send-email-sstabellini@kernel.org> <1497553787-3709-12-git-send-email-sstabellini@kernel.org> <15ea89f6-d46e-2495-1b52-d7290b47c478@oracle.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1724 Lines: 54 On Tue, 20 Jun 2017, Boris Ostrovsky wrote: > > @@ -499,6 +521,55 @@ static int pvcalls_back_accept(struct xenbus_device *dev, > > static int pvcalls_back_poll(struct xenbus_device *dev, > > struct xen_pvcalls_request *req) > > { > > + struct pvcalls_fedata *fedata; > > + struct sockpass_mapping *mappass; > > + struct xen_pvcalls_response *rsp; > > + struct inet_connection_sock *icsk; > > + struct request_sock_queue *queue; > > + unsigned long flags; > > + int ret; > > + bool data; > > + > > + fedata = dev_get_drvdata(&dev->dev); > > + > > + mappass = radix_tree_lookup(&fedata->socketpass_mappings, req->u.poll.id); > > + if (mappass == NULL) > > + return -EINVAL; > > + > > + /* > > + * Limitation of the current implementation: only support one > > + * concurrent accept or poll call on one socket. > > + */ > > + spin_lock_irqsave(&mappass->copy_lock, flags); > > + if (mappass->reqcopy.cmd != 0) { > > + ret = -EINTR; > > + goto out; > > + } > > + > > + mappass->reqcopy = *req; > > + icsk = inet_csk(mappass->sock->sk); > > + queue = &icsk->icsk_accept_queue; > > + spin_lock(&queue->rskq_lock); > > + data = queue->rskq_accept_head != NULL; > > + spin_unlock(&queue->rskq_lock); > > What is the purpose of the queue lock here? It is only there to protect accesses to rskq_accept_head. Functions that change rskq_accept_head take this lock, see for example net/ipv4/inet_connection_sock.c:inet_csk_reqsk_queue_add. I'll add an in-code comment. > > + if (data) { > > + mappass->reqcopy.cmd = 0; > > + ret = 0; > > + goto out; > > + } > > + spin_unlock_irqrestore(&mappass->copy_lock, flags); > > + > > + /* Tell the caller we don't need to send back a notification yet */ > > + return -1;