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=-12.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 autolearn=ham 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 5D3D8C432BE for ; Fri, 6 Aug 2021 20:17:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37DA6610E7 for ; Fri, 6 Aug 2021 20:17:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244895AbhHFUSH (ORCPT ); Fri, 6 Aug 2021 16:18:07 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:34231 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244840AbhHFUSG (ORCPT ); Fri, 6 Aug 2021 16:18:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1628281069; 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=AKEtsVz7WfVjpfJzqxqaNsm5zdfVw1TUqK/dikMgDyg=; b=OQqYZhFczGH6MYKOP8lN3nl3oacMiUftAEXLuro3l4wA0olmI5letaJw9qhkJJjVjUMby4 RHHF8qwq2uFZLtmp1puQb/zR+hwt2j0yHAfmYZHD1ppk5PdruJLxOXu4S0ipczUENDLsQ/ DeoMBhbaBGz3FCc5QQxtpZKCAetTu70= Received: from mail-oi1-f197.google.com (mail-oi1-f197.google.com [209.85.167.197]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-310-s1iCbYzqMVWLuEw3DSKwrg-1; Fri, 06 Aug 2021 16:17:48 -0400 X-MC-Unique: s1iCbYzqMVWLuEw3DSKwrg-1 Received: by mail-oi1-f197.google.com with SMTP id c6-20020aca35060000b029025c5504f461so4691891oia.22 for ; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=AKEtsVz7WfVjpfJzqxqaNsm5zdfVw1TUqK/dikMgDyg=; b=VDDPWO4R4urjWFjHp0c+vaHiX7LXmA78ls+2KKdsiqptZKjn3bYiEO6uUKRpCYiM3f VIAh8KJdc4mQNRufSTcDUKvE0+FkpyX5lzvboPAYcKaDvRQk2vjWM2vt3v/9QcESVOVa owIQmP2hb9zsCRmzgcCtdZt1kGL/CuK4/YJ3r+Wpv+DeT82RQ6yGRNcR+Lxs2ooAHTPo SAyCjVSoNQ5gtkDRffZzKgiLA9j4cj35WLHdNLu3WuhKsPlZdLN16TGTYw59Yt286BDL vhox8UXs8w+LkuHsCaV6G8aBwpCfn4kC4SWOqtF08Vn0rOyDjjKuZiBcynA8GhfYxRjk H3SA== X-Gm-Message-State: AOAM5302bHmO5aBqdIh1FrAywYfFFr3hYiPCaTG8aW77VMGQngVVPGrF Brbkx5ov4AxShODErkyxA1wX7HC402WdZf2eeOeFUj+VGYFqJztEG1niZFDktPgpdH+u2vIGZ6n RCXAHaw/5h52F X-Received: by 2002:a05:6808:b3c:: with SMTP id t28mr8529923oij.138.1628281067381; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwE/+radWlM0jhMSuigAQ6bd02/LEk6hSW+AqhKdTvsnB5GbjLi4CMMD+utdEDRsQXhnxTuVg== X-Received: by 2002:a05:6808:b3c:: with SMTP id t28mr8529912oij.138.1628281067157; Fri, 06 Aug 2021 13:17:47 -0700 (PDT) Received: from redhat.com ([198.99.80.109]) by smtp.gmail.com with ESMTPSA id 7sm164527oth.69.2021.08.06.13.17.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Aug 2021 13:17:46 -0700 (PDT) Date: Fri, 6 Aug 2021 14:17:45 -0600 From: Alex Williamson To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, peterx@redhat.com Subject: Re: [PATCH 3/7] vfio/pci: Use vfio_device_unmap_mapping_range() Message-ID: <20210806141745.1d8c3e0a.alex.williamson@redhat.com> In-Reply-To: <20210806010418.GF1672295@nvidia.com> References: <162818167535.1511194.6614962507750594786.stgit@omen> <162818325518.1511194.1243290800645603609.stgit@omen> <20210806010418.GF1672295@nvidia.com> X-Mailer: Claws Mail 3.18.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 5 Aug 2021 22:04:18 -0300 Jason Gunthorpe wrote: > On Thu, Aug 05, 2021 at 11:07:35AM -0600, Alex Williamson wrote: > > @@ -2281,15 +2143,13 @@ static int vfio_pci_try_zap_and_vma_lock_cb(struct pci_dev *pdev, void *data) > > > > vdev = container_of(device, struct vfio_pci_device, vdev); > > > > - /* > > - * Locking multiple devices is prone to deadlock, runaway and > > - * unwind if we hit contention. > > - */ > > - if (!vfio_pci_zap_and_vma_lock(vdev, true)) { > > + if (!down_write_trylock(&vdev->memory_lock)) { > > vfio_device_put(device); > > return -EBUSY; > > } > > Now that this is simplified so much, I wonder if we can drop the > memory_lock and just use the dev_set->lock? > > That avoids the whole down_write_trylock thing and makes it much more > understandable? Hmm, that would make this case a lot easier, but using a mutex, potentially shared across multiple devices, taken on every non-mmap read/write doesn't really feel like a good trade-off when we're currently using a per device rwsem to retain concurrency here. Thanks, Alex