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 6011EC25B07 for ; Fri, 5 Aug 2022 09:14:49 +0000 (UTC) Received: from localhost ([::1]:38796 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1oJtPs-00088q-5h for qemu-devel@archiver.kernel.org; Fri, 05 Aug 2022 05:14:48 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43770) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJtNW-00075u-OP for qemu-devel@nongnu.org; Fri, 05 Aug 2022 05:12:22 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:38962) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1oJtNT-0005Ix-LV for qemu-devel@nongnu.org; Fri, 05 Aug 2022 05:12:21 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1659690739; 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=GGqtG2J1JZraC0IgN8RgUPhg10NCUKiUeIC9FYGhBfk=; b=J0xRzdV8Z5tns5dK4yaREH7YB6QaAguM5tUumJtYbF4P7GxzFWR+w1Ekh0igRZI4+fZUCF 40svAjR66ZlbgNatFFTeo9J3BEK3fcZTw06lBoxyYBjgF7wc4O6ait/I9X4gu9k9wq4mWR Ft8yzGOm7rc2GsndpZv0JMs6rf2nFTc= 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-12-tr-VrffZPieNy4DtnCJghg-1; Fri, 05 Aug 2022 05:12:15 -0400 X-MC-Unique: tr-VrffZPieNy4DtnCJghg-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 969AC101A588; Fri, 5 Aug 2022 09:12:14 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.127]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8BFEE2166B26; Fri, 5 Aug 2022 09:12:11 +0000 (UTC) Date: Fri, 5 Aug 2022 11:12:10 +0200 From: Kevin Wolf To: Emanuele Giuseppe Esposito Cc: qemu-block@nongnu.org, Hanna Reitz , Paolo Bonzini , John Snow , Vladimir Sementsov-Ogievskiy , Wen Congyang , Xie Changlong , Markus Armbruster , Stefan Hajnoczi , Fam Zheng , qemu-devel@nongnu.org Subject: Re: [PATCH v10 14/21] jobs: protect job.aio_context with BQL and job_mutex Message-ID: References: <20220725073855.76049-1-eesposit@redhat.com> <20220725073855.76049-15-eesposit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220725073855.76049-15-eesposit@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 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: -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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=unavailable 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" Am 25.07.2022 um 09:38 hat Emanuele Giuseppe Esposito geschrieben: > In order to make it thread safe, implement a "fake rwlock", > where we allow reads under BQL *or* job_mutex held, but > writes only under BQL *and* job_mutex. Oh, so the "or BQL" part is only for job.aio_context? Okay. > The only write we have is in child_job_set_aio_ctx, which always > happens under drain (so the job is paused). > For this reason, introduce job_set_aio_context and make sure that > the context is set under BQL, job_mutex and drain. > Also make sure all other places where the aiocontext is read > are protected. > > Note: at this stage, job_{lock/unlock} and job lock guard macros > are *nop*. > > Suggested-by: Paolo Bonzini > Signed-off-by: Emanuele Giuseppe Esposito > Reviewed-by: Stefan Hajnoczi > --- > block/replication.c | 6 ++++-- > blockjob.c | 3 ++- > include/qemu/job.h | 19 ++++++++++++++++++- > job.c | 12 ++++++++++++ > 4 files changed, 36 insertions(+), 4 deletions(-) > > diff --git a/block/replication.c b/block/replication.c > index 55c8f894aa..2189863df1 100644 > --- a/block/replication.c > +++ b/block/replication.c > @@ -148,8 +148,10 @@ static void replication_close(BlockDriverState *bs) > } > if (s->stage == BLOCK_REPLICATION_FAILOVER) { > commit_job = &s->commit_job->job; > - assert(commit_job->aio_context == qemu_get_current_aio_context()); > - job_cancel_sync(commit_job, false); > + WITH_JOB_LOCK_GUARD() { > + assert(commit_job->aio_context == qemu_get_current_aio_context()); > + job_cancel_sync_locked(commit_job, false); > + } > } .bdrv_close runs under the BQL, so why is this needed? Maybe a GLOBAL_STATE_CODE() annotation would be helpful, though. > if (s->mode == REPLICATION_MODE_SECONDARY) { > diff --git a/blockjob.c b/blockjob.c > index 96fb9d9f73..9ff2727025 100644 > --- a/blockjob.c > +++ b/blockjob.c > @@ -162,12 +162,13 @@ static void child_job_set_aio_ctx(BdrvChild *c, AioContext *ctx, > bdrv_set_aio_context_ignore(sibling->bs, ctx, ignore); > } > > - job->job.aio_context = ctx; > + job_set_aio_context(&job->job, ctx); > } > > static AioContext *child_job_get_parent_aio_context(BdrvChild *c) > { > BlockJob *job = c->opaque; > + assert(qemu_in_main_thread()); Any reason not to use GLOBAL_STATE_CODE()? > return job->job.aio_context; > } > diff --git a/include/qemu/job.h b/include/qemu/job.h > index 5709e8d4a8..c144aabefc 100644 > --- a/include/qemu/job.h > +++ b/include/qemu/job.h > @@ -77,7 +77,12 @@ typedef struct Job { > > /** Protected by AioContext lock */ I think this section comment should move down below aio_context now. > - /** AioContext to run the job coroutine in */ > + /** > + * AioContext to run the job coroutine in. > + * This field can be read when holding either the BQL (so we are in > + * the main loop) or the job_mutex. > + * It can be only written when we hold *both* BQL and job_mutex. > + */ > AioContext *aio_context; > > /** Reference count of the block job */ > @@ -741,4 +746,16 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), > int job_finish_sync_locked(Job *job, void (*finish)(Job *, Error **errp), > Error **errp); > > +/** > + * Sets the @job->aio_context. > + * Called with job_mutex *not* held. > + * > + * This function must run in the main thread to protect against > + * concurrent read in job_finish_sync_locked(), Odd line break here in the middle of a sentence. > + * takes the job_mutex lock to protect against the read in > + * job_do_yield_locked(), and must be called when the coroutine > + * is quiescent. > + */ > +void job_set_aio_context(Job *job, AioContext *ctx); > + > #endif > diff --git a/job.c b/job.c > index ecec66b44e..0a857b1468 100644 > --- a/job.c > +++ b/job.c > @@ -394,6 +394,17 @@ Job *job_get(const char *id) > return job_get_locked(id); > } > > +void job_set_aio_context(Job *job, AioContext *ctx) > +{ > + /* protect against read in job_finish_sync_locked and job_start */ > + assert(qemu_in_main_thread()); Same question about GLOBAL_STATE_CODE(). > + /* protect against read in job_do_yield_locked */ > + JOB_LOCK_GUARD(); > + /* ensure the coroutine is quiescent while the AioContext is changed */ > + assert(job->pause_count > 0); job->pause_count only shows that pausing was requested. The coroutine is only really quiescent if job->busy == false, too. Or maybe job->paused is actually the one you want here. > + job->aio_context = ctx; > +} > + > /* Called with job_mutex *not* held. */ > static void job_sleep_timer_cb(void *opaque) > { > @@ -1376,6 +1387,7 @@ int job_finish_sync_locked(Job *job, > { > Error *local_err = NULL; > int ret; > + assert(qemu_in_main_thread()); > > job_ref_locked(job); Another GLOBAL_STATE_CODE()? Kevin