Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754360AbdFNGcM (ORCPT ); Wed, 14 Jun 2017 02:32:12 -0400 Received: from mx2.suse.de ([195.135.220.15]:39073 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750757AbdFNGcL (ORCPT ); Wed, 14 Jun 2017 02:32:11 -0400 Subject: Re: [PATCH v3 11/18] xen/pvcalls: implement accept command To: Stefano Stabellini Cc: xen-devel@lists.xen.org, linux-kernel@vger.kernel.org, boris.ostrovsky@oracle.com, Stefano Stabellini References: <1496431915-20774-1-git-send-email-sstabellini@kernel.org> <1496431915-20774-11-git-send-email-sstabellini@kernel.org> From: Juergen Gross Message-ID: <6749c353-5e63-77fb-2541-44703072e9ac@suse.com> Date: Wed, 14 Jun 2017 08:32:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5898 Lines: 186 On 14/06/17 02:47, Stefano Stabellini wrote: > On Tue, 13 Jun 2017, Juergen Gross wrote: >> On 02/06/17 21:31, Stefano Stabellini wrote: >>> Implement the accept command by calling inet_accept. To avoid blocking >>> in the kernel, call inet_accept(O_NONBLOCK) from a workqueue, which get >>> scheduled on sk_data_ready (for a passive socket, it means that there >>> are connections to accept). >>> >>> Use the reqcopy field to store the request. Accept the new socket from >>> the delayed work function, create a new sock_mapping for it, map >>> the indexes page and data ring, and reply to the other end. Allocate an >>> ioworker for the socket. >>> >>> Only support one outstanding blocking accept request for every socket at >>> any time. >>> >>> Add a field to sock_mapping to remember the passive socket from which an >>> active socket was created. >>> >>> Signed-off-by: Stefano Stabellini >>> CC: boris.ostrovsky@oracle.com >>> CC: jgross@suse.com >>> --- >>> drivers/xen/pvcalls-back.c | 109 ++++++++++++++++++++++++++++++++++++++++++++- >>> 1 file changed, 108 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c >>> index a75586e..f1173f4 100644 >>> --- a/drivers/xen/pvcalls-back.c >>> +++ b/drivers/xen/pvcalls-back.c >>> @@ -65,6 +65,7 @@ struct pvcalls_ioworker { >>> struct sock_mapping { >>> struct list_head list; >>> struct pvcalls_fedata *priv; >>> + struct sockpass_mapping *sockpass; >>> struct socket *sock; >>> uint64_t id; >>> grant_ref_t ref; >>> @@ -275,10 +276,79 @@ static int pvcalls_back_release(struct xenbus_device *dev, >>> >>> static void __pvcalls_back_accept(struct work_struct *work) >>> { >>> + struct sockpass_mapping *mappass = container_of( >>> + work, struct sockpass_mapping, register_work); >>> + struct sock_mapping *map; >>> + struct pvcalls_ioworker *iow; >>> + struct pvcalls_fedata *priv; >>> + struct socket *sock; >>> + struct xen_pvcalls_response *rsp; >>> + struct xen_pvcalls_request *req; >>> + int notify; >>> + int ret = -EINVAL; >>> + unsigned long flags; >>> + >>> + priv = mappass->priv; >>> + /* We only need to check the value of "cmd" atomically on read. */ >>> + spin_lock_irqsave(&mappass->copy_lock, flags); >>> + req = &mappass->reqcopy; >>> + if (req->cmd != PVCALLS_ACCEPT) { >>> + spin_unlock_irqrestore(&mappass->copy_lock, flags); >>> + return; >>> + } >>> + spin_unlock_irqrestore(&mappass->copy_lock, flags); >> >> What about: >> req = &mappass->reqcopy; >> if (ACCESS_ONCE(req->cmd) != PVCALLS_ACCEPT) >> return; >> >> I can't see the need for taking a lock here. > > Sure, good idea > > >>> + >>> + sock = sock_alloc(); >>> + if (sock == NULL) >>> + goto out_error; >>> + sock->type = mappass->sock->type; >>> + sock->ops = mappass->sock->ops; >>> + >>> + ret = inet_accept(mappass->sock, sock, O_NONBLOCK, true); >>> + if (ret == -EAGAIN) { >>> + sock_release(sock); >>> + goto out_error; >>> + } >>> + >>> + map = pvcalls_new_active_socket(priv, >>> + req->u.accept.id_new, >>> + req->u.accept.ref, >>> + req->u.accept.evtchn, >>> + sock); >>> + if (!map) { >>> + sock_release(sock); >>> + goto out_error; >>> + } >>> + >>> + map->sockpass = mappass; >>> + iow = &map->ioworker; >>> + atomic_inc(&map->read); >>> + atomic_inc(&map->io); >>> + queue_work_on(iow->cpu, iow->wq, &iow->register_work); >>> + >>> +out_error: >>> + rsp = RING_GET_RESPONSE(&priv->ring, priv->ring.rsp_prod_pvt++); >>> + rsp->req_id = req->req_id; >>> + rsp->cmd = req->cmd; >>> + rsp->u.accept.id = req->u.accept.id; >>> + rsp->ret = ret; >>> + RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&priv->ring, notify); >>> + if (notify) >>> + notify_remote_via_irq(priv->irq); >>> + >>> + spin_lock_irqsave(&mappass->copy_lock, flags); >>> + mappass->reqcopy.cmd = 0; >>> + spin_unlock_irqrestore(&mappass->copy_lock, flags); >> >> ACCESS_ONCE(mappass->reqcopy.cmd) = 0; > > OK > > >>> } >>> >>> static void pvcalls_pass_sk_data_ready(struct sock *sock) >>> { >>> + struct sockpass_mapping *mappass = sock->sk_user_data; >>> + >>> + if (mappass == NULL) >>> + return; >>> + >>> + queue_work(mappass->wq, &mappass->register_work); >>> } >>> >>> static int pvcalls_back_bind(struct xenbus_device *dev, >>> @@ -380,7 +450,44 @@ static int pvcalls_back_listen(struct xenbus_device *dev, >>> static int pvcalls_back_accept(struct xenbus_device *dev, >>> struct xen_pvcalls_request *req) >>> { >>> - return 0; >>> + struct pvcalls_fedata *priv; >>> + struct sockpass_mapping *mappass; >>> + int ret = -EINVAL; >>> + struct xen_pvcalls_response *rsp; >>> + unsigned long flags; >>> + >>> + priv = dev_get_drvdata(&dev->dev); >>> + >>> + mappass = radix_tree_lookup(&priv->socketpass_mappings, >>> + req->u.accept.id); >>> + if (mappass == NULL) >>> + goto out_error; >>> + >>> + /* >>> + * 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) { >>> + spin_unlock_irqrestore(&mappass->copy_lock, flags); >>> + ret = -EINTR; >>> + goto out_error; >>> + } >>> + >>> + mappass->reqcopy = *req; >> >> This time you need the lock, however you should use: >> >> ACCESS_ONCE(mappass->reqcopy) = *req; > > I don't think that guarantees atomic accesses to the cmd field of the > struct. Shouldn't this be: > > ACCESS_ONCE(mappass->reqcopy.cmd) = req->cmd; > mappass->reqcopy = *req; Hmm, what if the frontend changes cmd between those two accesses? You either need another local buffer or you have to copy cmd via ACCESS_ONCE() and the rest of *req separately (seems not to be that hard: its just cmd, req_id and u). BTW: Maybe you should use READ_ONCE() and WRITE_ONCE() instead of ACCESS_ONCE(), as those seem to be preferred nowadays. Juergen