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    <title>MongoDB Jira</title>
    <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-66353] Add documentation of concurrency rules for OperationContext::setAlwaysInterruptAtStepDownOrUp</title>
                <link>https://jira.mongodb.org/browse/SERVER-66353</link>
                <project id="10000" key="SERVER">Core Server</project>
                    <description>&lt;p&gt;The function&#160;&lt;a href=&quot;https://github.com/mongodb/mongo/blob/d5399825310e599b0cad119664c23e10d98ca5af/src/mongo/db/operation_context.h#L497&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;OperationContext::setAlwaysInterruptAtStepDownOrUp&lt;/a&gt;&#160;can be used to request that an operation context is interrupted/killed on replication state change.&lt;/p&gt;

&lt;p&gt;However, the function is dangerous to use because it is not synchronized internally with the RSTL, and does not insist that the caller is synchronized with the RSTL. This means that a node&apos;s view of it&apos;s replication state may change while the function is being called unless the RSTL is held by the caller, which causes subtle races because operations are registered to be killed only after state-change has already occurred. Here&apos;s an example of such a race:&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;
&lt;ol&gt;
	&lt;li&gt;Thread enters function to setAlwaysInterruptAtstepDownOrStepUp() on Op without holding the RSTL // Op not yet registered to be killed&lt;/li&gt;
	&lt;li&gt;Node steps down&lt;/li&gt;
	&lt;li&gt;setAlwaysInterruptAtstepDownOrStepUp() completes // Op registered to be killed now&lt;/li&gt;
	&lt;li&gt;Op continues running anyways because of race above&lt;/li&gt;
&lt;/ol&gt;


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

&lt;p&gt;We have seen many BFs with races of the above form. As a first step to improve the situation, in this ticket, let&apos;s add some documentation emphasizing the lack of built-in-RSTL synchronization with this function, and express the risk of concurrent replication-state-change clearly. Let&apos;s also consider adding _UNSAFE to the end of the function name, which would follow the pattern of functions on the replication coordinator that are not synchronized with the RSTL (see &lt;a href=&quot;https://github.com/mongodb/mongo/blob/d5399825310e599b0cad119664c23e10d98ca5af/src/mongo/db/repl/replication_coordinator_impl.h#L152).&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/blob/d5399825310e599b0cad119664c23e10d98ca5af/src/mongo/db/repl/replication_coordinator_impl.h#L152).&lt;/a&gt;&#160;&lt;/p&gt;

&lt;p&gt;&#160;&lt;/p&gt;</description>
                <environment></environment>
        <key id="2043425">SERVER-66353</key>
            <summary>Add documentation of concurrency rules for OperationContext::setAlwaysInterruptAtStepDownOrUp</summary>
                <type id="4" iconUrl="https://jira.mongodb.org/secure/viewavatar?size=xsmall&amp;avatarId=14710&amp;avatarType=issuetype">Improvement</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="george.wangensteen@mongodb.com">George Wangensteen</assignee>
                                    <reporter username="george.wangensteen@mongodb.com">George Wangensteen</reporter>
                        <labels>
                    </labels>
                <created>Tue, 10 May 2022 15:16:51 +0000</created>
                <updated>Sun, 29 Oct 2023 21:38:24 +0000</updated>
                            <resolved>Tue, 24 May 2022 14:46:20 +0000</resolved>
                                                    <fixVersion>6.1.0-rc0</fixVersion>
                                                        <votes>0</votes>
                                    <watches>4</watches>
                                                                                                                <comments>
                            <comment id="4567985" author="xgen-internal-githook" created="Mon, 23 May 2022 23:16:39 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;George Wangensteen&apos;, &apos;email&apos;: &apos;george.wangensteen@mongodb.com&apos;, &apos;username&apos;: &apos;gewa24&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66353&quot; title=&quot;Add documentation of concurrency rules for OperationContext::setAlwaysInterruptAtStepDownOrUp&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66353&quot;&gt;&lt;del&gt;SERVER-66353&lt;/del&gt;&lt;/a&gt; Add concurrency information to OperationContext::setAlwaysInterruptAtStepDownOrUp&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/mongodb/mongo/commit/c904c1853594468bbf60cc330d89a5b89b0e6365&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/mongodb/mongo/commit/c904c1853594468bbf60cc330d89a5b89b0e6365&lt;/a&gt;&lt;/p&gt;</comment>
                            <comment id="4567984" author="xgen-internal-githook" created="Mon, 23 May 2022 23:16:34 +0000"  >&lt;p&gt;Author:&lt;/p&gt;
{&apos;name&apos;: &apos;George Wangensteen&apos;, &apos;email&apos;: &apos;george.wangensteen@mongodb.com&apos;, &apos;username&apos;: &apos;gewa24&apos;}
&lt;p&gt;Message: &lt;a href=&quot;https://jira.mongodb.org/browse/SERVER-66353&quot; title=&quot;Add documentation of concurrency rules for OperationContext::setAlwaysInterruptAtStepDownOrUp&quot; class=&quot;issue-link&quot; data-issue-key=&quot;SERVER-66353&quot;&gt;&lt;del&gt;SERVER-66353&lt;/del&gt;&lt;/a&gt; Add concurrency information to OperationContext::setAlwaysInterruptAtStepDownOrUp&lt;br/&gt;
Branch: master&lt;br/&gt;
&lt;a href=&quot;https://github.com/10gen/mongo-enterprise-modules/commit/9d41a167bf45646f5112d082acc26ed8d38e8236&quot; class=&quot;external-link&quot; target=&quot;_blank&quot; rel=&quot;nofollow noopener&quot;&gt;https://github.com/10gen/mongo-enterprise-modules/commit/9d41a167bf45646f5112d082acc26ed8d38e8236&lt;/a&gt;&lt;/p&gt;</comment>
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                    <name>Related</name>
                                                                <inwardlinks description="is related to">
                                        <issuelink>
            <issuekey id="1865473">SERVER-59719</issuekey>
        </issuelink>
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