From patchwork Fri Apr 9 13:29:45 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Max Reitz X-Patchwork-Id: 1464357 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=GarAcZne; dkim-atps=neutral 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 ozlabs.org (Postfix) with ESMTPS id 4FGzYb1D4qz9sWD for ; Fri, 9 Apr 2021 23:31:31 +1000 (AEST) Received: from localhost ([::1]:47498 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lUrEP-00033p-2R for incoming@patchwork.ozlabs.org; Fri, 09 Apr 2021 09:31:29 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:35180) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUrD0-00032T-0N for qemu-devel@nongnu.org; Fri, 09 Apr 2021 09:30:03 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:49512) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUrCx-0006Ik-4g for qemu-devel@nongnu.org; Fri, 09 Apr 2021 09:30:01 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617974996; 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=wsnsP07uN5j3BvYwTMv1RswmbCtmj25/r931U5r3zLI=; b=GarAcZne+JjK0NYVkEpdSV6wTp3bo+1q7vT7VyVSEjzA8d8VMzx0vQv1ipU8NQG1Enwkfc 9sQYJz3dTJ6A0XMBG0J7RpX3aBnDOH9cUJfP467dm19TS46ifFB1yLxnZAlwq8UcY4jiWz yHVYGXZUxExBUeZyAUlkcqxDNZwRBxE= 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-388-8VHsGn52NHG9jyyxOE8cSA-1; Fri, 09 Apr 2021 09:29:54 -0400 X-MC-Unique: 8VHsGn52NHG9jyyxOE8cSA-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 891271A8A60; Fri, 9 Apr 2021 13:29:53 +0000 (UTC) Received: from localhost (ovpn-114-67.ams2.redhat.com [10.36.114.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 015025D9E3; Fri, 9 Apr 2021 13:29:52 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Subject: [PATCH v2 1/3] job: Add job_wait_unpaused() for block-job-complete Date: Fri, 9 Apr 2021 15:29:45 +0200 Message-Id: <20210409132948.195511-2-mreitz@redhat.com> In-Reply-To: <20210409132948.195511-1-mreitz@redhat.com> References: <20210409132948.195511-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=170.10.133.124; envelope-from=mreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 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_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Vladimir Sementsov-Ogievskiy , John Snow , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" block-job-complete can only be applied when the job is READY, not when it is on STANDBY (ready, but paused). Draining a job technically pauses it (which makes a READY job enter STANDBY), and ending the drained section does not synchronously resume it, but only schedules the job, which will then be resumed. So attempting to complete a job immediately after a drained section may sometimes fail. That is bad at least because users cannot really work nicely around this: A job may be paused and resumed at any time, so waiting for the job to be in the READY state and then issuing a block-job-complete poses a TOCTTOU problem. The only way around it would be to issue block-job-complete until it no longer fails due to the job being in the STANDBY state, but that would not be nice. We can solve the problem by allowing block-job-complete to be invoked on jobs that are on STANDBY, if that status is the result of a drained section (not because the user has paused the job), and that section has ended. That is, if the job is on STANDBY, but scheduled to be resumed. Perhaps we could actually just directly allow this, seeing that mirror is the only user of ready/complete, and that mirror_complete() could probably work under the given circumstances, but there may be many side effects to consider. It is simpler to add a function job_wait_unpaused() that waits for the job to be resumed (under said circumstances), and to make qmp_block_job_complete() use it to delay job_complete() until then. Note that for the future, we probably want to make block-job-complete a coroutine QMP handler, so instead of polling job_wait_unpaused() would yield and have job_pause_point() wake it up. That would get around the problem of nested polling, which is currently the reason for returning an error when job->pause_point > 0. Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1945635 Signed-off-by: Max Reitz --- include/qemu/job.h | 15 +++++++++++++ blockdev.c | 3 +++ job.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 71 insertions(+) diff --git a/include/qemu/job.h b/include/qemu/job.h index efc6fa7544..cf3082b6d7 100644 --- a/include/qemu/job.h +++ b/include/qemu/job.h @@ -563,4 +563,19 @@ void job_dismiss(Job **job, Error **errp); */ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp); +/** + * If the job has been paused because of a drained section, and that + * section has ended, wait until the job is resumed. + * + * Return 0 if the job is not paused, or if it has been successfully + * resumed. + * Return an error if the job has been paused in such a way that + * waiting will not resume it, i.e. if it has been paused by the user, + * or if it is still drained. + * + * Callers must be in the home AioContext and hold the AioContext lock + * of job->aio_context. + */ +int job_wait_unpaused(Job *job, Error **errp); + #endif diff --git a/blockdev.c b/blockdev.c index a57590aae4..c0cc2fa364 100644 --- a/blockdev.c +++ b/blockdev.c @@ -3414,6 +3414,9 @@ void qmp_block_job_complete(const char *device, Error **errp) return; } + if (job_wait_unpaused(&job->job, errp) < 0) { + return; + } trace_qmp_block_job_complete(job); job_complete(&job->job, errp); aio_context_release(aio_context); diff --git a/job.c b/job.c index 289edee143..fbccd4b32a 100644 --- a/job.c +++ b/job.c @@ -505,6 +505,7 @@ void coroutine_fn job_pause_point(Job *job) job_do_yield(job, -1); job->paused = false; job_state_transition(job, status); + aio_wait_kick(); } if (job->driver->resume) { @@ -1023,3 +1024,55 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp) job_unref(job); return ret; } + +int job_wait_unpaused(Job *job, Error **errp) +{ + /* + * Only run this function from the main context, because this is + * what we need, and this way we do not have to think about what + * happens if the user concurrently pauses the job from the main + * monitor. + */ + assert(qemu_get_current_aio_context() == qemu_get_aio_context()); + + /* + * Quick path (e.g. so we do not get an error if pause_count > 0 + * but the job is not even paused) + */ + if (!job->paused) { + return 0; + } + + /* If the user has paused the job, waiting will not help */ + if (job->user_paused) { + error_setg(errp, "Job '%s' has been paused and needs to be explicitly " + "resumed", job->id); + return -EBUSY; + } + + /* + * Similarly, if the job is still drained, waiting may not help + * either: If the drain came from an IO thread, waiting would + * probably help. However, if the drain came from the main thread + * (which may be possible if the QMP handler calling this function + * has been invoked by BDRV_POLL_WHILE() from a drain_begin), then + * waiting will only deadlock. + * Better be safe and return an error. Drains from IO threads + * probably do not occur anyway. + */ + if (job->pause_count > 0) { + error_setg(errp, "Job '%s' is blocked and cannot be unpaused", job->id); + return -EBUSY; + } + + /* + * This function is specifically for waiting for a job to be + * resumed after a drained section. Ending the drained section + * includes a job_enter(), which schedules the job loop to be run, + * and once it does, job->paused will be cleared. Therefore, we + * do not need to invoke job_enter() here. + */ + AIO_WAIT_WHILE(job->aio_context, job->paused); + + return 0; +}