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([2a02:8071:5055:3f20:7ad9:a400:6d51:83e6]) by smtp.gmail.com with ESMTPSA id r17sm47618wmq.11.2021.11.10.07.05.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 10 Nov 2021 07:05:58 -0800 (PST) Message-ID: Date: Wed, 10 Nov 2021 16:05:57 +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 2/7] block: Manipulate children list in .attach/.detach To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20211104103849.46855-1-hreitz@redhat.com> <20211104103849.46855-3-hreitz@redhat.com> From: Hanna Reitz In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=hreitz@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=170.10.129.124; envelope-from=hreitz@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -51 X-Spam_score: -5.2 X-Spam_bar: ----- X-Spam_report: (-5.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.699, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-1.678, 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=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: , Cc: Kevin Wolf , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 10.11.21 13:46, Vladimir Sementsov-Ogievskiy wrote: > 04.11.2021 13:38, Hanna Reitz wrote: >> The children list is specific to BDS parents.  We should not modify it >> in the general children modification code, but let BDS parents deal with >> it in their .attach() and .detach() methods. >> >> This also has the advantage that a BdrvChild is removed from the >> children list before its .bs pointer can become NULL.  BDS parents >> generally assume that their children's .bs pointer is never NULL, so >> this is actually a bug fix. >> >> Signed-off-by: Hanna Reitz >> --- >>   block.c | 9 +++++---- >>   1 file changed, 5 insertions(+), 4 deletions(-) >> >> diff --git a/block.c b/block.c >> index 580cb77a70..243ae206b5 100644 >> --- a/block.c >> +++ b/block.c >> @@ -1387,6 +1387,8 @@ static void bdrv_child_cb_attach(BdrvChild *child) >>   { >>       BlockDriverState *bs = child->opaque; >>   +    QLIST_INSERT_HEAD(&bs->children, child, next); >> + >>       if (child->role & BDRV_CHILD_COW) { >>           bdrv_backing_attach(child); >>       } >> @@ -1403,6 +1405,8 @@ static void bdrv_child_cb_detach(BdrvChild *child) >>       } >>         bdrv_unapply_subtree_drain(child, bs); >> + >> +    QLIST_REMOVE(child, next); >>   } >>     static int bdrv_child_cb_update_filename(BdrvChild *c, >> BlockDriverState *base, >> @@ -2747,7 +2751,7 @@ static void bdrv_child_free(void *opaque) >>   static void bdrv_remove_empty_child(BdrvChild *child) >>   { >>       assert(!child->bs); >> -    QLIST_SAFE_REMOVE(child, next); >> +    assert(!child->next.le_prev); /* not in children list */ >>       bdrv_child_free(child); >>   } >>   @@ -2913,7 +2917,6 @@ static int >> bdrv_attach_child_noperm(BlockDriverState *parent_bs, >>           return ret; >>       } >>   -    QLIST_INSERT_HEAD(&parent_bs->children, *child, next); > > The following comment become stale. We should remove it too. With > comment removed: Ah, right, thanks! > Reviewed-by: Vladimir Sementsov-Ogievskiy