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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 919A1C433E0 for ; Wed, 20 Jan 2021 10:08:00 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id C243E2332A for ; Wed, 20 Jan 2021 10:07:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C243E2332A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; 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bh=p4OU06fIjte01YaOlC7ag3UYsT+eEe/mHJxn+5H1ogA=; b=aae6MT/fAeUIbA3mQcyD/W3be+FLYpJtD1IQYqQ30/qUlfW4WOETUo+yCaNUoD/aB2v+2/ RAyjJLF1+vhK4ZH1VHau0j5EYGsixKT6lY0S8SHAmioxGFgPnjlGBmhNv3JFKxfXnM0Kz9 sbaj4m2dG9dOn1YrUh6MHkDH0iv6MLQ= 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-439-ZXyFI2hXNDCV2Ykio6qK0A-1; Wed, 20 Jan 2021 05:06:42 -0500 X-MC-Unique: ZXyFI2hXNDCV2Ykio6qK0A-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B7CA9802B48; Wed, 20 Jan 2021 10:06:41 +0000 (UTC) Received: from merkur.fritz.box (ovpn-114-210.ams2.redhat.com [10.36.114.210]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3266D2BFE3; Wed, 20 Jan 2021 10:06:40 +0000 (UTC) Date: Wed, 20 Jan 2021 11:06:38 +0100 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH v2 12/36] block: refactor bdrv_child* permission functions Message-ID: <20210120100638.GC5521@merkur.fritz.box> References: <20201127144522.29991-1-vsementsov@virtuozzo.com> <20201127144522.29991-13-vsementsov@virtuozzo.com> <20210119180909.GK5012@merkur.fritz.box> <0b634f73-b997-d72d-e7ab-3a1dcdfeb509@virtuozzo.com> <20210120090954.GB5521@merkur.fritz.box> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 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 Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.195, 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_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable 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: qemu-block@nongnu.org, armbru@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, den@openvz.org, jsnow@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 20.01.2021 um 10:56 hat Vladimir Sementsov-Ogievskiy geschrieben: > 20.01.2021 12:09, Kevin Wolf wrote: > > Am 19.01.2021 um 19:30 hat Vladimir Sementsov-Ogievskiy geschrieben: > > > 19.01.2021 21:09, Kevin Wolf wrote: > > > > Am 27.11.2020 um 15:44 hat Vladimir Sementsov-Ogievskiy geschrieben: > > > > > Split out non-recursive parts, and refactor as block graph transaction > > > > > action. > > > > > > > > > > Signed-off-by: Vladimir Sementsov-Ogievskiy > > > > > --- > > > > > block.c | 79 ++++++++++++++++++++++++++++++++++++++++++--------------- > > > > > 1 file changed, 59 insertions(+), 20 deletions(-) > > > > > > > > > > diff --git a/block.c b/block.c > > > > > index a756f3e8ad..7267b4a3e9 100644 > > > > > --- a/block.c > > > > > +++ b/block.c > > > > > @@ -48,6 +48,7 @@ > > > > > #include "qemu/timer.h" > > > > > #include "qemu/cutils.h" > > > > > #include "qemu/id.h" > > > > > +#include "qemu/transactions.h" > > > > > #include "block/coroutines.h" > > > > > #ifdef CONFIG_BSD > > > > > @@ -2033,6 +2034,61 @@ static void bdrv_child_perm(BlockDriverState *bs, BlockDriverState *child_bs, > > > > > } > > > > > } > > > > > +static void bdrv_child_set_perm_commit(void *opaque) > > > > > +{ > > > > > + BdrvChild *c = opaque; > > > > > + > > > > > + c->has_backup_perm = false; > > > > > +} > > > > > + > > > > > +static void bdrv_child_set_perm_abort(void *opaque) > > > > > +{ > > > > > + BdrvChild *c = opaque; > > > > > + /* > > > > > + * We may have child->has_backup_perm unset at this point, as in case of > > > > > + * _check_ stage of permission update failure we may _check_ not the whole > > > > > + * subtree. Still, _abort_ is called on the whole subtree anyway. > > > > > + */ > > > > > + if (c->has_backup_perm) { > > > > > + c->perm = c->backup_perm; > > > > > + c->shared_perm = c->backup_shared_perm; > > > > > + c->has_backup_perm = false; > > > > > + } > > > > > +} > > > > > + > > > > > +static TransactionActionDrv bdrv_child_set_pem_drv = { > > > > > + .abort = bdrv_child_set_perm_abort, > > > > > + .commit = bdrv_child_set_perm_commit, > > > > > +}; > > > > > + > > > > > +/* > > > > > + * With tran=NULL needs to be followed by direct call to either > > > > > + * bdrv_child_set_perm_commit() or bdrv_child_set_perm_abort(). > > > > > + * > > > > > + * With non-NUll tran needs to be followed by tran_abort() or tran_commit() > > > > > > > > s/NUll/NULL/ > > > > > > > > > + * instead. > > > > > + */ > > > > > +static void bdrv_child_set_perm_safe(BdrvChild *c, uint64_t perm, > > > > > + uint64_t shared, GSList **tran) > > > > > +{ > > > > > + if (!c->has_backup_perm) { > > > > > + c->has_backup_perm = true; > > > > > + c->backup_perm = c->perm; > > > > > + c->backup_shared_perm = c->shared_perm; > > > > > + } > > > > > > > > This is the obvious refactoring at this point, and it's fine as such. > > > > > > > > However, when you start to actually use tran (and in new places), it > > > > means that I have to check that we can never end up here recursively > > > > with a different tran. > > > > > > I don't follow.. Which different tran do you mean? > > > > Any really. At this point in the series, nothing passes a non-NULL tran > > yet. When you add the first user, it is only a local transaction for a > > single node. If something else called bdrv_child_set_perm_safe() on the > > same node before the transaction has completed, the result would be > > broken. > > But this problem is preexisting: if someone call bdrv_child_set_perm > twice on the same node during one update operation, c->backup* will be > rewritten. > > > > > So reviewing/understanding this change (and actually developing it in > > the first place) means going through all the code that ends up inside > > the transaction and making sure that we never try to change permissions > > for the same node a second time in any context. > > I think we do it, when find same node several times during update. And > that is fixed in "[PATCH v2 15/36] block: use topological sort for > permission update", when we move to topological sorted list. Ah, fair. Knowing that the state is broken before this patch makes things easier in a way... Kevin