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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C6CFFC4361B for ; Tue, 15 Dec 2020 15:35:20 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 826942246B for ; Tue, 15 Dec 2020 15:35:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 826942246B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.54329.94321 (Exim 4.92) (envelope-from ) id 1kpCLa-0004Nz-48; Tue, 15 Dec 2020 15:34:42 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 54329.94321; Tue, 15 Dec 2020 15:34:42 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kpCLa-0004Ns-13; Tue, 15 Dec 2020 15:34:42 +0000 Received: by outflank-mailman (input) for mailman id 54329; Tue, 15 Dec 2020 15:34:40 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kpCLY-0004Nn-2D for xen-devel@lists.xenproject.org; Tue, 15 Dec 2020 15:34:40 +0000 Received: from us-smtp-delivery-124.mimecast.com (unknown [63.128.21.124]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id 0313667e-2a1d-4491-8ab0-c5aa8646a448; Tue, 15 Dec 2020 15:34:37 +0000 (UTC) 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-266-mB2UIrCmOIiyNDQ8CYSesw-1; Tue, 15 Dec 2020 10:34:35 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 13D2F81CB08; Tue, 15 Dec 2020 15:34:10 +0000 (UTC) Received: from merkur.fritz.box (ovpn-117-65.ams2.redhat.com [10.36.117.65]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6E72060854; Tue, 15 Dec 2020 15:34:07 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 0313667e-2a1d-4491-8ab0-c5aa8646a448 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608046477; 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=JGAmSk/5NnCmnaOU3RbF+dwSsWHRiNNwBCIq+AYP6jw=; b=PhE6w4KWWN2LfiRWpdmF+aJF6pN0oNjuQs+Ftei7VZ7CYlEqZx3OGj9yzdrDajjRbYZX+I 3kUq3GrHhVbAiSlTST91eZlcy3NlLDNrjGtLadOMQ5KTC4vXfSXWxI8hG/hnCtB8we2qOS 1PGWLSwDmRDAJNtxIFEx2Na97jknEpw= X-MC-Unique: mB2UIrCmOIiyNDQ8CYSesw-1 Date: Tue, 15 Dec 2020 16:34:05 +0100 From: Kevin Wolf To: Sergio Lopez Cc: qemu-devel@nongnu.org, Stefano Stabellini , qemu-block@nongnu.org, Anthony Perard , xen-devel@lists.xenproject.org, Paul Durrant , "Michael S. Tsirkin" , Stefan Hajnoczi , Fam Zheng , Eric Blake , Paolo Bonzini , Max Reitz Subject: Re: [PATCH v2 4/4] block: Close block exports in two steps Message-ID: <20201215153405.GF8185@merkur.fritz.box> References: <20201214170519.223781-1-slp@redhat.com> <20201214170519.223781-5-slp@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201214170519.223781-5-slp@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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 Am 14.12.2020 um 18:05 hat Sergio Lopez geschrieben: > There's a cross-dependency between closing the block exports and > draining the block layer. The latter needs that we close all export's > client connections to ensure they won't queue more requests, but the > exports may have coroutines yielding in the block layer, which implies > they can't be fully closed until we drain it. A coroutine that yielded must have some way to be reentered. So I guess the quesiton becomes why they aren't reentered until drain. We do process events: AIO_WAIT_WHILE(NULL, blk_exp_has_type(type)); So in theory, anything that would finalise the block export closing should still execute. What is the difference that drain makes compared to a simple AIO_WAIT_WHILE, so that coroutine are reentered during drain, but not during AIO_WAIT_WHILE? This is an even more interesting question because the NBD server isn't a block node nor a BdrvChildClass implementation, so it shouldn't even notice a drain operation. Kevin > To break this cross-dependency, this change adds a "bool wait" > argument to blk_exp_close_all() and blk_exp_close_all_type(), so > callers can decide whether they want to wait for the exports to be > fully quiesced, or just return after requesting them to shut down. > > Then, in bdrv_close_all we make two calls, one without waiting to > close all client connections, and another after draining the block > layer, this time waiting for the exports to be fully quiesced. > > RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1900505 > Signed-off-by: Sergio Lopez > --- > block.c | 20 +++++++++++++++++++- > block/export/export.c | 10 ++++++---- > blockdev-nbd.c | 2 +- > include/block/export.h | 4 ++-- > qemu-nbd.c | 2 +- > stubs/blk-exp-close-all.c | 2 +- > 6 files changed, 30 insertions(+), 10 deletions(-) > > diff --git a/block.c b/block.c > index bc8a66ab6e..41db70ac07 100644 > --- a/block.c > +++ b/block.c > @@ -4472,13 +4472,31 @@ static void bdrv_close(BlockDriverState *bs) > void bdrv_close_all(void) > { > assert(job_next(NULL) == NULL); > - blk_exp_close_all(); > + > + /* > + * There's a cross-dependency between closing the block exports and > + * draining the block layer. The latter needs that we close all export's > + * client connections to ensure they won't queue more requests, but the > + * exports may have coroutines yielding in the block layer, which implies > + * they can't be fully closed until we drain it. > + * > + * Make a first call to close all export's client connections, without > + * waiting for each export to be fully quiesced. > + */ > + blk_exp_close_all(false); > > /* Drop references from requests still in flight, such as canceled block > * jobs whose AIO context has not been polled yet */ > bdrv_drain_all(); > > blk_remove_all_bs(); > + > + /* > + * Make a second call to shut down the exports, this time waiting for them > + * to be fully quiesced. > + */ > + blk_exp_close_all(true); > + > blockdev_close_all_bdrv_states(); > > assert(QTAILQ_EMPTY(&all_bdrv_states)); > diff --git a/block/export/export.c b/block/export/export.c > index bad6f21b1c..0124ebd9f9 100644 > --- a/block/export/export.c > +++ b/block/export/export.c > @@ -280,7 +280,7 @@ static bool blk_exp_has_type(BlockExportType type) > } > > /* type == BLOCK_EXPORT_TYPE__MAX for all types */ > -void blk_exp_close_all_type(BlockExportType type) > +void blk_exp_close_all_type(BlockExportType type, bool wait) > { > BlockExport *exp, *next; > > @@ -293,12 +293,14 @@ void blk_exp_close_all_type(BlockExportType type) > blk_exp_request_shutdown(exp); > } > > - AIO_WAIT_WHILE(NULL, blk_exp_has_type(type)); > + if (wait) { > + AIO_WAIT_WHILE(NULL, blk_exp_has_type(type)); > + } > } > > -void blk_exp_close_all(void) > +void blk_exp_close_all(bool wait) > { > - blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX); > + blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX, wait); > } > > void qmp_block_export_add(BlockExportOptions *export, Error **errp) > diff --git a/blockdev-nbd.c b/blockdev-nbd.c > index d8443d235b..d71d4da7c2 100644 > --- a/blockdev-nbd.c > +++ b/blockdev-nbd.c > @@ -266,7 +266,7 @@ void qmp_nbd_server_stop(Error **errp) > return; > } > > - blk_exp_close_all_type(BLOCK_EXPORT_TYPE_NBD); > + blk_exp_close_all_type(BLOCK_EXPORT_TYPE_NBD, true); > > nbd_server_free(nbd_server); > nbd_server = NULL; > diff --git a/include/block/export.h b/include/block/export.h > index 7feb02e10d..71c25928ce 100644 > --- a/include/block/export.h > +++ b/include/block/export.h > @@ -83,7 +83,7 @@ BlockExport *blk_exp_find(const char *id); > void blk_exp_ref(BlockExport *exp); > void blk_exp_unref(BlockExport *exp); > void blk_exp_request_shutdown(BlockExport *exp); > -void blk_exp_close_all(void); > -void blk_exp_close_all_type(BlockExportType type); > +void blk_exp_close_all(bool wait); > +void blk_exp_close_all_type(BlockExportType type, bool wait); > > #endif > diff --git a/qemu-nbd.c b/qemu-nbd.c > index a7075c5419..928f4466f6 100644 > --- a/qemu-nbd.c > +++ b/qemu-nbd.c > @@ -1122,7 +1122,7 @@ int main(int argc, char **argv) > do { > main_loop_wait(false); > if (state == TERMINATE) { > - blk_exp_close_all(); > + blk_exp_close_all(true); > state = TERMINATED; > } > } while (state != TERMINATED); > diff --git a/stubs/blk-exp-close-all.c b/stubs/blk-exp-close-all.c > index 1c71316763..ecd0ce611f 100644 > --- a/stubs/blk-exp-close-all.c > +++ b/stubs/blk-exp-close-all.c > @@ -2,6 +2,6 @@ > #include "block/export.h" > > /* Only used in programs that support block exports (libblockdev.fa) */ > -void blk_exp_close_all(void) > +void blk_exp_close_all(bool wait) > { > } > -- > 2.26.2 >