From patchwork Mon Mar 14 13:37:04 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Emanuele Giuseppe Esposito X-Patchwork-Id: 12780167 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 23ECBC433EF for ; Mon, 14 Mar 2022 13:52:10 +0000 (UTC) Received: from localhost ([::1]:38200 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nTl7J-0001oZ-6W for qemu-devel@archiver.kernel.org; Mon, 14 Mar 2022 09:52:09 -0400 Received: from eggs.gnu.org ([209.51.188.92]:43030) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nTkt9-0006r7-GJ for qemu-devel@nongnu.org; Mon, 14 Mar 2022 09:37:31 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:56312) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nTksz-0001bx-1V for qemu-devel@nongnu.org; Mon, 14 Mar 2022 09:37:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647265040; 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=8Qku4dctQ4sjVMV749sTmhR8eTXFOw9zShugX0BUtow=; b=VpW6Dy6fy1nUrplJXwFUge8cPcOG/3ZTnwcfPIzIQNW3QJ8BANXzlW9JJBDlOySilpdhGX Ulvw8w/AgYhZauZVwZ+TsBQCkfAeaXnpf2ja8cvjWFY3SpoBxFyAHIOpFIJAibLRaQwnyi 0F935TaaxMDHE+QeMxhPGxndN9QzSIo= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-664-i3Slgx5IPwGH8XNLfdU9kg-1; Mon, 14 Mar 2022 09:37:19 -0400 X-MC-Unique: i3Slgx5IPwGH8XNLfdU9kg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 94DCB2999B2B; Mon, 14 Mar 2022 13:37:18 +0000 (UTC) Received: from virtlab701.virt.lab.eng.bos.redhat.com (virtlab701.virt.lab.eng.bos.redhat.com [10.19.152.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 47BFB403144; Mon, 14 Mar 2022 13:37:18 +0000 (UTC) From: Emanuele Giuseppe Esposito To: qemu-block@nongnu.org Subject: [PATCH v6 15/18] job: detect change of aiocontext within job coroutine Date: Mon, 14 Mar 2022 09:37:04 -0400 Message-Id: <20220314133707.2206082-16-eesposit@redhat.com> In-Reply-To: <20220314133707.2206082-1-eesposit@redhat.com> References: <20220314133707.2206082-1-eesposit@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=eesposit@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Received-SPF: pass client-ip=170.10.133.124; envelope-from=eesposit@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 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_NONE=-0.0001, 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: Kevin Wolf , Fam Zheng , Vladimir Sementsov-Ogievskiy , Wen Congyang , Xie Changlong , Markus Armbruster , qemu-devel@nongnu.org, Hanna Reitz , Stefan Hajnoczi , Paolo Bonzini , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" From: Paolo Bonzini We want to make sure access of job->aio_context is always done under either BQL or job_mutex. The problem is that using aio_co_enter(job->aiocontext, job->co) in job_start and job_enter_cond makes the coroutine immediately resume, so we can't hold the job lock. And caching it is not safe either, as it might change. job_start is under BQL, so it can freely read job->aiocontext, but job_enter_cond is not. In order to fix this, use aio_co_wake(): the advantage is that it won't use job->aiocontext, but the main disadvantage is that it won't be able to detect a change of job AioContext. Calling bdrv_try_set_aio_context() will issue the following calls (simplified): * in terms of bdrv callbacks: .drained_begin -> .set_aio_context -> .drained_end * in terms of child_job functions: child_job_drained_begin -> child_job_set_aio_context -> child_job_drained_end * in terms of job functions: job_pause_locked -> job_set_aio_context -> job_resume_locked We can see that after setting the new aio_context, job_resume_locked calls again job_enter_cond, which then invokes aio_co_wake(). But while job->aiocontext has been set in job_set_aio_context, job->co->ctx has not changed, so the coroutine would be entering in the wrong aiocontext. Using aio_co_schedule in job_resume_locked() might seem as a valid alternative, but the problem is that the bh resuming the coroutine is not scheduled immediately, and if in the meanwhile another bdrv_try_set_aio_context() is run (see test_propagate_mirror() in test-block-iothread.c), we would have the first schedule in the wrong aiocontext, and the second set of drains won't even manage to schedule the coroutine, as job->busy would still be true from the previous job_resume_locked(). The solution is to stick with aio_co_wake(), but then detect every time the coroutine resumes back from yielding if job->aio_context has changed. If so, we can reschedule it to the new context. Check for the aiocontext change in job_do_yield_locked because: 1) aio_co_reschedule_self requires to be in the running coroutine 2) since child_job_set_aio_context allows changing the aiocontext only while the job is paused, this is the exact place where the coroutine resumes, before running JobDriver's code. Reviewed-by: Stefan Hajnoczi Signed-off-by: Paolo Bonzini --- job.c | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) diff --git a/job.c b/job.c index 89c0e6bed9..10a5981748 100644 --- a/job.c +++ b/job.c @@ -543,11 +543,12 @@ void job_enter_cond_locked(Job *job, bool(*fn)(Job *job)) return; } - assert(!job->deferred_to_main_loop); timer_del(&job->sleep_timer); job->busy = true; real_job_unlock(); - aio_co_enter(job->aio_context, job->co); + job_unlock(); + aio_co_wake(job->co); + job_lock(); } void job_enter(Job *job) @@ -568,6 +569,8 @@ void job_enter(Job *job) */ static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns) { + AioContext *next_aio_context; + real_job_lock(); if (ns != -1) { timer_mod(&job->sleep_timer, ns); @@ -579,6 +582,20 @@ static void coroutine_fn job_do_yield_locked(Job *job, uint64_t ns) qemu_coroutine_yield(); job_lock(); + next_aio_context = job->aio_context; + /* + * Coroutine has resumed, but in the meanwhile the job AioContext + * might have changed via bdrv_try_set_aio_context(), so we need to move + * the coroutine too in the new aiocontext. + */ + while (qemu_get_current_aio_context() != next_aio_context) { + job_unlock(); + aio_co_reschedule_self(next_aio_context); + job_lock(); + next_aio_context = job->aio_context; + } + + /* Set by job_enter_cond_locked() before re-entering the coroutine. */ assert(job->busy); } @@ -680,7 +697,6 @@ void job_resume_locked(Job *job) if (job->pause_count) { return; } - /* kick only if no timer is pending */ job_enter_cond_locked(job, job_timer_not_pending_locked); } @@ -1122,6 +1138,8 @@ static void coroutine_fn job_co_entry(void *opaque) void job_start(Job *job) { + assert(qemu_in_main_thread()); + WITH_JOB_LOCK_GUARD() { assert(job && !job_started(job) && job->paused && job->driver && job->driver->run);