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    <link>https://jira.mongodb.org</link>
    <description>This file is an XML representation of an issue</description>
    <language>en-us</language>    <build-info>
        <version>9.7.1</version>
        <build-number>970001</build-number>
        <build-date>13-04-2023</build-date>
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<item>
            <title>[SERVER-76448] Data race on rename collection participant</title>
                <link>https://jira.mongodb.org/browse/SERVER-76448</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;When &lt;tt&gt;shardsvr_rename_collection_participant&lt;/tt&gt; command is called, first it calls &lt;a href=&quot;https://github.com/10gen/mongo/blob/274cb477d2a1b64ac81b85e9f1b3172387ce0184/src/mongo/db/s/shardsvr_rename_collection_participant_command.cpp#L101&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;getOrCreate&lt;/a&gt;, which returns an instance of a {{renameCollectionParticipant }}running&#160;asynchronously, then it &lt;a href=&quot;https://github.com/10gen/mongo/blob/274cb477d2a1b64ac81b85e9f1b3172387ce0184/src/mongo/db/s/shardsvr_rename_collection_participant_command.cpp#L102&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;checks&lt;/a&gt; if the parameters of the request are the same than the parameters of the given instance (to ensure idempotency).&lt;/p&gt;

&lt;p&gt;Since the check is done while the &lt;tt&gt;renameCollectionParticipant&lt;/tt&gt; is being executed on another thread, there is a data race over &lt;tt&gt;_doc&lt;/tt&gt; attribute:&lt;/p&gt;
&lt;ul&gt;
	&lt;li&gt;During the check we &lt;a href=&quot;https://github.com/10gen/mongo/blob/274cb477d2a1b64ac81b85e9f1b3172387ce0184/src/mongo/db/s/rename_collection_participant_service.cpp#L146&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;read _&lt;tt&gt;doc&lt;/tt&gt;&lt;/a&gt;&lt;/li&gt;
	&lt;li&gt;The &lt;tt&gt;renameCollectionParticipant::run&lt;/tt&gt; operation &lt;a href=&quot;https://github.com/10gen/mongo/blob/274cb477d2a1b64ac81b85e9f1b3172387ce0184/src/mongo/db/s/rename_collection_participant_service.cpp#L207&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;updates _doc&lt;/a&gt;.&lt;/li&gt;
&lt;/ul&gt;


&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;CONSEQUENCES OF THE BUG:&lt;/p&gt;

&lt;p&gt;In case of reading a defective &lt;tt&gt;_doc&lt;/tt&gt; value due to a data race the DDL coordinator will retry the command &lt;a href=&quot;https://github.com/10gen/mongo/blob/7cc71f7d5f29a5850a4d186b9554df3dcb407117/src/mongo/db/s/sharding_ddl_coordinator.cpp#L378-L380&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;here&lt;/a&gt;.&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;

&lt;p&gt;A suggestion to fix this bug is to add a const attribute (which could be called &lt;tt&gt;_request&lt;/tt&gt;) and initiate it on the constructor using the &lt;tt&gt;_doc&lt;/tt&gt; value, similar to what &lt;tt&gt;RenameCollectionCoordinator&lt;/tt&gt; already does &lt;a href=&quot;https://github.com/10gen/mongo/blob/7cc71f7d5f29a5850a4d186b9554df3dcb407117/src/mongo/db/s/rename_collection_coordinator.cpp#L134&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;(1)&lt;/a&gt; &lt;a href=&quot;https://github.com/10gen/mongo/blob/7cc71f7d5f29a5850a4d186b9554df3dcb407117/src/mongo/db/s/rename_collection_coordinator.cpp#L136-L148&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;(2)&lt;/a&gt;.&lt;/p&gt;</description>
                <environment></environment>
        <key id="2322112">SERVER-76448</key>
            <summary>Data race on rename collection participant</summary>
                <type id="1" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14703&amp;avatarType=issuetype">Bug</type>
                                            <priority id="3" iconUrl="https://jira.mongodb.org/images/icons/priorities/major.svg">Major - P3</priority>
                        <status id="6" iconUrl="https://jira.mongodb.org/images/icons/statuses/closed.png" description="The issue is considered finished, the resolution is correct. Issues which are closed can be reopened.">Closed</status>
                    <statusCategory id="3" key="done" colorName="success"/>
                                    <resolution id="13201">Fixed</resolution>
                                        <assignee username="silvia.surroca@mongodb.com">Silvia Surroca</assignee>
                                    <reporter username="silvia.surroca@mongodb.com">Silvia Surroca</reporter>
                        <labels>
                    </labels>
                <created>Mon, 24 Apr 2023 11:19:28 +0000</created>
                <updated>Sun, 29 Oct 2023 21:22:37 +0000</updated>
                            <resolved>Wed, 26 Apr 2023 06:21:40 +0000</resolved>
                                    <version>5.0.0</version>
                    <version>6.0.0</version>
                    <version>7.0.0-rc0</version>
                                    <fixVersion>7.1.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>3</watches>
                                                                                                                <comments>
                            <comment id="5375977" author="xgen-internal-githook" created="Wed, 26 Apr 2023 06:53:18 +0000"  >&lt;p&gt;Author: &lt;/p&gt;
{&apos;name&apos;: &apos;Silvia Surroca&apos;, &apos;email&apos;: &apos;silvia.surroca@mongodb.com&apos;, &apos;username&apos;: &apos;silviasuhu&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-76448&quot; title=&quot;Data race on rename collection participant&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-76448&quot;&gt;&lt;del&gt;SERVER-76448&lt;/del&gt;&lt;/a&gt; Fix race condition on rename collection participant service&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/ab714adf0e71005e00ed42367f41ba864b4e6170&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/ab714adf0e71005e00ed42367f41ba864b4e6170&lt;/a&gt;&lt;/p&gt;</comment>
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