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([2a04:ee41:4:31cb:e591:1e1e:abde:a8f1]) by smtp.gmail.com with ESMTPSA id do16sm1960970ejc.190.2021.12.16.08.05.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Dec 2021 08:05:25 -0800 (PST) Message-ID: <937d15e5-4ba5-af84-f3bf-a4aa828f9d82@redhat.com> Date: Thu, 16 Dec 2021 17:05:24 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH v5 10/31] block.c: modify .attach and .detach callbacks of child_of_bds To: Hanna Reitz , qemu-block@nongnu.org References: <20211124064418.3120601-1-eesposit@redhat.com> <20211124064418.3120601-11-eesposit@redhat.com> From: Emanuele Giuseppe Esposito In-Reply-To: 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 Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit 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: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.718, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.034, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , Vladimir Sementsov-Ogievskiy , =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= , Eduardo Habkost , Juan Quintela , qemu-devel@nongnu.org, John Snow , Richard Henderson , Markus Armbruster , "Dr. David Alan Gilbert" , Stefan Hajnoczi , Paolo Bonzini , Eric Blake Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 16/12/2021 15:57, Hanna Reitz wrote: > On 24.11.21 07:43, Emanuele Giuseppe Esposito wrote: >> According to the assertions put in the previous patch, we should >> first drain and then modify the ->children list. In this way >> we prevent other iothreads to read the list while it is being >> updated. >> >> In this case, moving the drain won't cause any harm, because >> child is a parameter of the drain function so it will still be >> included in the operation, despite not being in the list. > > Sounds good. Uhm.. I don't think this is useful at all. I was thinking to drop this patch in v6. My plans on subtree drains, ->children and ->parent lists are explained in "Removal of Aiocontext lock and usage of subtree drains in aborted transactions" https://patchew.org/QEMU/20211213104014.69858-1-eesposit@redhat.com/ And as I say there, commit d736f119da makes sure that it is safe to modify the graph even side a bdrv_subtree_drained_begin/end() section. So this should be unnecessary. Thank you, Emanuele > >> Signed-off-by: Emanuele Giuseppe Esposito >> --- >>   block.c | 5 ++--- >>   1 file changed, 2 insertions(+), 3 deletions(-) >> >> diff --git a/block.c b/block.c >> index 522a273140..5516c84ec4 100644 >> --- a/block.c >> +++ b/block.c >> @@ -1416,6 +1416,7 @@ static void bdrv_child_cb_attach(BdrvChild *child) >>   { >>       BlockDriverState *bs = child->opaque; >> +    bdrv_apply_subtree_drain(child, bs); >>       assert_bdrv_graph_writable(bs); >>       QLIST_INSERT_HEAD(&bs->children, child, next); >> @@ -1423,7 +1424,6 @@ static void bdrv_child_cb_attach(BdrvChild *child) >>           bdrv_backing_attach(child); >>       } >> -    bdrv_apply_subtree_drain(child, bs); > > I think we should also remove the empty line above. > > Hanna > >>   } >>   static void bdrv_child_cb_detach(BdrvChild *child) >> @@ -1434,10 +1434,9 @@ static void bdrv_child_cb_detach(BdrvChild *child) >>           bdrv_backing_detach(child); >>       } >> -    bdrv_unapply_subtree_drain(child, bs); >> - >>       assert_bdrv_graph_writable(bs); >>       QLIST_REMOVE(child, next); >> +    bdrv_unapply_subtree_drain(child, bs); >>   } >>   static int bdrv_child_cb_update_filename(BdrvChild *c, >> BlockDriverState *base, >