From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46702) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dVrP1-0004Yn-6I for qemu-devel@nongnu.org; Thu, 13 Jul 2017 23:36:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dVrOy-0001Gx-3L for qemu-devel@nongnu.org; Thu, 13 Jul 2017 23:36:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60946) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dVrOx-0001Ge-QP for qemu-devel@nongnu.org; Thu, 13 Jul 2017 23:36:24 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8EBC074862 for ; Fri, 14 Jul 2017 03:36:22 +0000 (UTC) Date: Fri, 14 Jul 2017 11:36:19 +0800 From: Peter Xu Message-ID: <20170714033619.GG27284@pxdev.xzpeter.org> References: <20170713115649.11853-1-dgilbert@redhat.com> <20170713115649.11853-4-dgilbert@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20170713115649.11853-4-dgilbert@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 3/5] migration/rdma: Allow cancelling while waiting for wrid List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert (git)" Cc: qemu-devel@nongnu.org, quintela@redhat.com, lvivier@redhat.com On Thu, Jul 13, 2017 at 12:56:47PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" > > When waiting for a WRID, if the other side dies we end up waiting > for ever with no way to cancel the migration. > Cure this by poll()ing the fd first with a timeout and checking > error flags and migration state. > > Signed-off-by: Dr. David Alan Gilbert > --- > migration/rdma.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++------ > 1 file changed, 46 insertions(+), 6 deletions(-) > > diff --git a/migration/rdma.c b/migration/rdma.c > index 6111e10c70..30f5542b49 100644 > --- a/migration/rdma.c > +++ b/migration/rdma.c > @@ -1466,6 +1466,50 @@ static uint64_t qemu_rdma_poll(RDMAContext *rdma, uint64_t *wr_id_out, > return 0; > } > > +/* Wait for activity on the completion channel. > + * Returns 0 on success, none-0 on error. > + */ > +static int qemu_rdma_wait_comp_channel(RDMAContext *rdma) > +{ > + /* > + * Coroutine doesn't start until migration_fd_process_incoming() > + * so don't yield unless we know we're running inside of a coroutine. > + */ > + if (rdma->migration_started_on_destination) { > + yield_until_fd_readable(rdma->comp_channel->fd); > + } else { > + /* This is the source side, we're in a separate thread > + * or destination prior to migration_fd_process_incoming() > + * we can't yield; so we have to poll the fd. > + * But we need to be able to handle 'cancel' or an error > + * without hanging forever. > + */ > + while (!rdma->error_state && !rdma->received_error) { > + GPollFD pfds[1]; > + pfds[0].fd = rdma->comp_channel->fd; > + pfds[0].events = G_IO_IN | G_IO_HUP | G_IO_ERR; > + /* 0.1s timeout, should be fine for a 'cancel' */ > + switch (qemu_poll_ns(pfds, 1, 100 * 1000 * 1000)) { > + case 1: /* fd active */ > + return 0; > + > + case 0: /* Timeout, go around again */ > + break; > + > + default: /* Error of some type */ > + return -1; > + } > + > + if (migrate_get_current()->state == MIGRATION_STATUS_CANCELLING) { > + /* Bail out and let the cancellation happen */ > + return -EPIPE; > + } > + } > + } > + > + return rdma->error_state || rdma->received_error; Just to note that this operation will return either 0 or 1, but not anything <0 (most RDMA codes are using <0 as error, and error_state should be <= 0 always iiuc). But as the comment for this function, it's fine. > +} > + > /* > * Block until the next work request has completed. > * > @@ -1513,12 +1557,8 @@ static int qemu_rdma_block_for_wrid(RDMAContext *rdma, int wrid_requested, > } > > while (1) { > - /* > - * Coroutine doesn't start until migration_fd_process_incoming() > - * so don't yield unless we know we're running inside of a coroutine. > - */ > - if (rdma->migration_started_on_destination) { > - yield_until_fd_readable(rdma->comp_channel->fd); > + if (qemu_rdma_wait_comp_channel(rdma)) { Do we want something like: ret = -EIO; Here? Or capture the return code of qemu_rdma_wait_comp_channel() (but then we need to make sure its return code is <0)? I guess "ret" is still zero, and it means this function will return with zero as well even timed out? Thanks, -- Peter Xu