From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54285) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dV85g-0006b4-J3 for qemu-devel@nongnu.org; Tue, 11 Jul 2017 23:13:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dV85d-0005ak-7Y for qemu-devel@nongnu.org; Tue, 11 Jul 2017 23:13:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:58320) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dV85d-0005a3-0u for qemu-devel@nongnu.org; Tue, 11 Jul 2017 23:13:25 -0400 Date: Wed, 12 Jul 2017 11:13:17 +0800 From: Peter Xu Message-ID: <20170712031317.GC29326@pxdev.xzpeter.org> References: <20170704184915.31586-1-dgilbert@redhat.com> <20170704184915.31586-2-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170704184915.31586-2-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/5] migration/rdma: Fix race on source List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert (git)" Cc: qemu-devel@nongnu.org, michael@hinespot.com, quintela@redhat.com, lvivier@redhat.com, berrange@redhat.com On Tue, Jul 04, 2017 at 07:49:11PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > Fix a race where the destination might try and send the source a > WRID_READY before the source has done a post-recv for it. > > rdma_post_recv has to happen after the qp exists, and we're > OK since we've already called qemu_rdma_source_init that calls > qemu_alloc_qp. Though I am not very familiar with the whole RDMA path, this makes sense to me. > > This corresponds to: > https://bugzilla.redhat.com/show_bug.cgi?id=1285044 > > The race can be triggered by adding a few ms wait before this > post_recv_control (which was originally due to me turning on loads of > debug). > > Signed-off-by: Dr. David Alan Gilbert Reviewed-by: Peter Xu > --- > migration/rdma.c | 12 ++++++------ > 1 file changed, 6 insertions(+), 6 deletions(-) > > diff --git a/migration/rdma.c b/migration/rdma.c > index c6bc607a03..6111e10c70 100644 > --- a/migration/rdma.c > +++ b/migration/rdma.c > @@ -2365,6 +2365,12 @@ static int qemu_rdma_connect(RDMAContext *rdma, Error **errp) > > caps_to_network(&cap); > > + ret = qemu_rdma_post_recv_control(rdma, RDMA_WRID_READY); > + if (ret) { > + ERROR(errp, "posting second control recv"); > + goto err_rdma_source_connect; > + } > + > ret = rdma_connect(rdma->cm_id, &conn_param); > if (ret) { > perror("rdma_connect"); > @@ -2405,12 +2411,6 @@ static int qemu_rdma_connect(RDMAContext *rdma, Error **errp) > > rdma_ack_cm_event(cm_event); > > - ret = qemu_rdma_post_recv_control(rdma, RDMA_WRID_READY); > - if (ret) { > - ERROR(errp, "posting second control recv!"); > - goto err_rdma_source_connect; > - } > - > rdma->control_ready_expected = 1; > rdma->nb_sent = 0; > return 0; > -- > 2.13.0 > -- Peter Xu