From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E379C433B4 for ; Tue, 11 May 2021 11:32:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3083B61430 for ; Tue, 11 May 2021 11:32:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231425AbhEKLdL (ORCPT ); Tue, 11 May 2021 07:33:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:40243 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231409AbhEKLdL (ORCPT ); Tue, 11 May 2021 07:33:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620732724; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=noaKl91GZtjSUFV6u8sREF0taPucQNZsvq/1PFe3aI8=; b=CdUqEDq/A7d5FTJOvhLhWrHGq3Pkr10o9K8S+qPwoZQV+yPKfAonmO+2KTdH07oY0/0oPc kV9ON2vGDpPk1/XOc0Z8jSwhTPv2FUYIGjpEPDob4DjoAUpa69wjPtG4QkAO7AFUX/J00I qwIt5eANUU3BnJk1/ytuVEPv9uBM/W8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-212-QStnA6OgOfGIT25KW3zosw-1; Tue, 11 May 2021 07:31:59 -0400 X-MC-Unique: QStnA6OgOfGIT25KW3zosw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id C473410066E8; Tue, 11 May 2021 11:31:58 +0000 (UTC) Received: from gondolin.fritz.box (ovpn-113-172.ams2.redhat.com [10.36.113.172]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7447362499; Tue, 11 May 2021 11:31:57 +0000 (UTC) Date: Tue, 11 May 2021 13:31:54 +0200 From: Cornelia Huck To: Eric Farman Cc: Matthew Rosato , Halil Pasic , Jared Rossi , linux-s390@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC PATCH v5 3/3] vfio-ccw: Serialize FSM IDLE state with I/O completion Message-ID: <20210511133154.66440087.cohuck@redhat.com> In-Reply-To: <20210510205646.1845844-4-farman@linux.ibm.com> References: <20210510205646.1845844-1-farman@linux.ibm.com> <20210510205646.1845844-4-farman@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 10 May 2021 22:56:46 +0200 Eric Farman wrote: > Today, the stacked call to vfio_ccw_sch_io_todo() does three things: > > 1) Update a solicited IRB with CP information, and release the CP > if the interrupt was the end of a START operation. > 2) Copy the IRB data into the io_region, under the protection of > the io_mutex > 3) Reset the vfio-ccw FSM state to IDLE to acknowledge that > vfio-ccw can accept more work. > > The trouble is that step 3 is (A) invoked for both solicited and > unsolicited interrupts, and (B) sitting after the mutex for step 2. > This second piece becomes a problem if it processes an interrupt > for a CLEAR SUBCHANNEL while another thread initiates a START, > thus allowing the CP and FSM states to get out of sync. That is: > > CPU 1 CPU 2 > fsm_do_clear() > fsm_irq() > fsm_io_request() > vfio_ccw_sch_io_todo() > fsm_io_helper() > > Since the FSM state and CP should be kept in sync, let's make a > note when the CP is released, and rely on that as an indication > that the FSM should also be reset at the end of this routine and > open up the device for more work. > > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_drv.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c > index 8c625b530035..ef39182edab5 100644 > --- a/drivers/s390/cio/vfio_ccw_drv.c > +++ b/drivers/s390/cio/vfio_ccw_drv.c > @@ -85,7 +85,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) > { > struct vfio_ccw_private *private; > struct irb *irb; > - bool is_final; > + bool is_final, is_finished = false; "is_finished" does not really say what is finished; maybe call it "cp_is_finished"? > > private = container_of(work, struct vfio_ccw_private, io_work); > irb = &private->irb; > @@ -94,14 +94,16 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) > (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT)); > if (scsw_is_solicited(&irb->scsw)) { > cp_update_scsw(&private->cp, &irb->scsw); > - if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) > + if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) { > cp_free(&private->cp); > + is_finished = true; > + } > } > mutex_lock(&private->io_mutex); > memcpy(private->io_region->irb_area, irb, sizeof(*irb)); > mutex_unlock(&private->io_mutex); > > - if (private->mdev && is_final) > + if (private->mdev && is_finished) Maybe add a comment? /* * Reset to idle if processing of a channel program * has finished; but do not overwrite a possible * processing state if we got a final interrupt for hsch * or csch. */ Otherwise, I see us scratching our heads again in a few months :) > private->state = VFIO_CCW_STATE_IDLE; > > if (private->io_trigger) Patch looks good to me.