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=-15.8 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 6B953C433B4 for ; Wed, 21 Apr 2021 10:26:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 349A16140F for ; Wed, 21 Apr 2021 10:26:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238390AbhDUK1K (ORCPT ); Wed, 21 Apr 2021 06:27:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:55906 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238301AbhDUK1J (ORCPT ); Wed, 21 Apr 2021 06:27:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1619000796; 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=bjglrOe7R8vsi2nemsozqNa/o3uknpFaJaifsKU0JIc=; b=TxUrpOCF3AZ72YfIYfvVoUXlrW8kg8Engk8fPft7zIEm+qp0o3kLuGqVhfQnmq7x3XtGLw usgRCCqa53FUMw0hvK/HPMuygVsIJgCmCOT5I/YFsHUGP2ehLHLoXcoHEXtN5L7g5dN/av +JexAm3FNLrcb5OiSLblBj+aHWM5cPo= 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-402-Yqu4U4LhNAu4XZj8RLpP3Q-1; Wed, 21 Apr 2021 06:25:34 -0400 X-MC-Unique: Yqu4U4LhNAu4XZj8RLpP3Q-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 58CB3107ACE4; Wed, 21 Apr 2021 10:25:33 +0000 (UTC) Received: from gondolin.fritz.box (ovpn-112-160.ams2.redhat.com [10.36.112.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id F0A7D10016FE; Wed, 21 Apr 2021 10:25:31 +0000 (UTC) Date: Wed, 21 Apr 2021 12:25:29 +0200 From: Cornelia Huck To: Eric Farman Cc: Halil Pasic , Matthew Rosato , Jared Rossi , linux-s390@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC PATCH v4 4/4] vfio-ccw: Reset FSM state to IDLE before io_mutex Message-ID: <20210421122529.6e373a39.cohuck@redhat.com> In-Reply-To: <20210413182410.1396170-5-farman@linux.ibm.com> References: <20210413182410.1396170-1-farman@linux.ibm.com> <20210413182410.1396170-5-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 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Tue, 13 Apr 2021 20:24:10 +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() > fsm_io_helper() > vfio_ccw_sch_io_todo() > fsm_irq() > vfio_ccw_sch_io_todo() > > Let's move the reset of the FSM state to the point where the > channel_program struct is cleaned up, which is only done for > solicited interrupts anyway. > > Signed-off-by: Eric Farman > --- > drivers/s390/cio/vfio_ccw_drv.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c > index 8c625b530035..e51318f23ca8 100644 > --- a/drivers/s390/cio/vfio_ccw_drv.c > +++ b/drivers/s390/cio/vfio_ccw_drv.c > @@ -94,16 +94,15 @@ 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); > + private->state = VFIO_CCW_STATE_IDLE; > + } > } > mutex_lock(&private->io_mutex); > memcpy(private->io_region->irb_area, irb, sizeof(*irb)); > mutex_unlock(&private->io_mutex); > > - if (private->mdev && is_final) > - private->state = VFIO_CCW_STATE_IDLE; Isn't that re-allowing new I/O requests a bit too early? Maybe remember that we had a final I/O interrupt for an I/O request and only change the state in this case? > - > if (private->io_trigger) > eventfd_signal(private->io_trigger, 1); > }