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 1677EC678D7 for ; Mon, 16 Jan 2023 15:58:00 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1pHRrM-0001b6-72; Mon, 16 Jan 2023 10:57:20 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pHRrK-0001aa-59 for qemu-devel@nongnu.org; Mon, 16 Jan 2023 10:57:18 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1pHRrI-0004ay-Mp for qemu-devel@nongnu.org; Mon, 16 Jan 2023 10:57:17 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1673884634; 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=Sxj+dL2dOvFjOWqoGO6mjospFfJjWDnfPtyWOpB79YQ=; b=KbfZaZjdYCaGF6KK4t6JLh598K7S/0ymoCKzotECbMD2UQgfo2yR+XAjuQ6FbgZzLOprVJ y70lTG9/mtX4YW7pjRXOh2IrMdeezU3rvzV9C57/oQyk8ULSsxCENpbny7FUEKxnrjPm12 69egJxjk/OgCBdlwAVqaQEC2HlBIRew= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-633-aLO1HYwSMU22O3fFMZl61g-1; Mon, 16 Jan 2023 10:57:13 -0500 X-MC-Unique: aLO1HYwSMU22O3fFMZl61g-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 939C6101A521; Mon, 16 Jan 2023 15:57:12 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.101]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C2D6D2166B26; Mon, 16 Jan 2023 15:57:11 +0000 (UTC) Date: Mon, 16 Jan 2023 16:57:10 +0100 From: Kevin Wolf To: Paolo Bonzini Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, eesposit@redhat.com Subject: Re: [PATCH 07/15] block-backend: enter aio coroutine only after drain Message-ID: References: <20221212125920.248567-1-pbonzini@redhat.com> <20221212125920.248567-8-pbonzini@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221212125920.248567-8-pbonzini@redhat.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.6 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 12.12.2022 um 13:59 hat Paolo Bonzini geschrieben: > When called from within (another) coroutine, aio_co_enter will not > enter a coroutine immediately; instead the new coroutine is scheduled > to run after qemu_coroutine_yield(). This however might cause the > currently-running coroutine to yield without having raised blk->in_flight. I assume you're talking about the blk_aio_prwv() path here. However, calling blk_inc_in_flight() is the very first thing it does (before even calling bdrv_coroutine_enter -> aio_co_enter), so I don't understand how it could happen that it yields before increasing the counter. > If it was a ->drained_begin() callback who scheduled the coroutine, Which one? The one that executes blk_aio_prwv()? > bdrv_drained_begin() might exit without waiting for the I/O operation > to finish. Right now, this is masked by unnecessary polling done by > bdrv_drained_begin() after the callbacks return, but it is wrong and > a latent bug. > > So, ensure that blk_inc_in_flight() and blk_wait_while_drained() > are called before aio_co_enter(). To do so, pull the call to > blk_wait_while_drained() out of the blk_co_do_* functions, which are > called from the AIO coroutines, and place them separately in the public > blk_co_* functions and in blk_aio_prwv. You can't call blk_wait_while_drained() in blk_aio_prwv() because the latter isn't a coroutine_fn. > Signed-off-by: Paolo Bonzini > --- > block/block-backend.c | 16 +++++++--------- > 1 file changed, 7 insertions(+), 9 deletions(-) Kevin