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 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 15504C433EF for ; Fri, 4 Mar 2022 10:54:17 +0000 (UTC) Received: from localhost ([::1]:36820 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nQ5Zg-0005y7-6D for qemu-devel@archiver.kernel.org; Fri, 04 Mar 2022 05:54:16 -0500 Received: from eggs.gnu.org ([209.51.188.92]:48258) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nQ5Xd-0004GC-Q7 for qemu-devel@nongnu.org; Fri, 04 Mar 2022 05:52:09 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:53195) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nQ5Xc-0003Y7-2D for qemu-devel@nongnu.org; Fri, 04 Mar 2022 05:52:09 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646391127; 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: in-reply-to:in-reply-to:references:references; bh=ZMvOywKOef3Pv9qprJJSdWmu/krwUls4eyRmjn3sm5c=; b=eQD1YV9ND7WCdtiyJnjgiPKixE/gwJdn/+t2H3QdTJ5poeYWt7kKpnwiWBhxcQ9si6sIek uPgGNfJd6t+MrANWoN5fKi0vi0LtC0QgWv/kKxJF+jgsEmpwkXs1wLFTkYNxjyGBzvAia7 2omjyNEFbmxwN00PMSE0kOrE9pTiBEs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-158-uaC9ru7OPpChb8Cs5GIwVA-1; Fri, 04 Mar 2022 05:52:06 -0500 X-MC-Unique: uaC9ru7OPpChb8Cs5GIwVA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3BABE180A08E; Fri, 4 Mar 2022 10:52:03 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.38]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C2E46842D6; Fri, 4 Mar 2022 10:51:44 +0000 (UTC) Date: Fri, 4 Mar 2022 11:51:43 +0100 From: Kevin Wolf To: Emanuele Giuseppe Esposito Subject: Re: [PATCH v8 00/31] block layer: split block APIs in global state and I/O Message-ID: References: <20220303151616.325444-1-eesposit@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220303151616.325444-1-eesposit@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Fam Zheng , Eduardo Habkost , Vladimir Sementsov-Ogievskiy , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , qemu-block@nongnu.org, Juan Quintela , qemu-devel@nongnu.org, John Snow , Richard Henderson , Markus Armbruster , "Dr. David Alan Gilbert" , Hanna Reitz , Stefan Hajnoczi , Paolo Bonzini , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 03.03.2022 um 16:15 hat Emanuele Giuseppe Esposito geschrieben: > Currently, block layer APIs like block.h contain a mix of > functions that are either running in the main loop and under the > BQL, or are thread-safe functions and run in iothreads performing I/O. > The functions running under BQL also take care of modifying the > block graph, by using drain and/or aio_context_acquire/release. > This makes it very confusing to understand where each function > runs, and what assumptions it provided with regards to thread > safety. > > We call the functions running under BQL "global state (GS) API", and > distinguish them from the thread-safe "I/O API". > > The aim of this series is to split the relevant block headers in > global state and I/O sub-headers. The division will be done in > this way: > header.h will be split in header-global-state.h, header-io.h and > header-common.h. The latter will just contain the data structures > needed by header-global-state and header-io, and common helpers > that are neither in GS nor in I/O. header.h will remain for > legacy and to avoid changing all includes in all QEMU c files, > but will only include the two new headers. No function shall be > added in header.c . > Once we split all relevant headers, it will be much easier to see what > uses the AioContext lock and remove it, which is the overall main > goal of this and other series that I posted/will post. > > In addition to splitting the relevant headers shown in this series, > it is also very helpful splitting the function pointers in some > block structures, to understand what runs under AioContext lock and > what doesn't. This is what patches 21-27 do. > > Each function in the GS API will have an assertion, checking > that it is always running under BQL. > I/O functions are instead thread safe (or so should be), meaning > that they *can* run under BQL, but also in an iothread in another > AioContext. Therefore they do not provide any assertion, and > need to be audited manually to verify the correctness. > > Adding assetions has helped finding 2 bugs already, as shown in > my series "Migration: fix missing iothread locking". > > Tested this series by running unit tests, qemu-iotests and qtests > (x86_64). > Some functions in the GS API are used everywhere but not > properly tested. Therefore their assertion is never actually run in > the tests, so despite my very careful auditing, it is not impossible > to exclude that some will trigger while actually using QEMU. > > Patch 1 introduces qemu_in_main_thread(), the function used in > all assertions. This had to be introduced otherwise all unit tests > would fail, since they run in the main loop but use the code in > stubs/iothread.c > Patches 2-27 (with the exception of patch 9-10, that are an additional > assert) are all structured in the same way: first we split the header > and in the next (or same, if small) patch we add assertions. > Patch 28-31 take care instead of the block layer permission API, > fixing some bugs where they are used in I/O functions. > > This serie depends on my previous serie "block layer: permission API > refactoring in preparation to the API split" > > Based-on: <20220209105452.1694545-1-eesposit@redhat.com> > > Signed-off-by: Emanuele Giuseppe Esposito > --- > v8: > bdrv_get_full_backing_filename to GLOBAL_STATE_CODE > blk_iostatus_is_enabled in IO_CODE > blk_iostatus_set_err in IO_CODE > bdrv_apply_auto_read_only in IO_CODE > bdrv_can_set_read_only in IO_CODE > blk_drain to GLOBAL_STATE_CODE Thanks, fixed up the unintentional changes to bdrv_op_blocker_is_empty() and bdrv_op_unblock_all() as discussed on IRC, and applied to the block branch. Kevin