<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/REC-html40/loose.dtd">
<html lang="en" style="--code-editor-font: var(--default-mono-font, "GitLab Mono"), JetBrains Mono, Menlo, DejaVu Sans Mono, Liberation Mono, Consolas, Ubuntu Mono, Courier New, andale mono, lucida console, monospace;">
<head>
<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
<title>
GitLab
</title>
<style data-premailer="ignore" type="text/css">
a { color: #1068bf; }
</style>
<style>img {
max-width: 100%; height: auto;
}
body {
font-size: .875rem;
}
body {
-webkit-text-shadow: rgba(255,255,255,.01) 0 0 1px;
}
body {
font-family: "GitLab Sans",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Noto Sans",Ubuntu,Cantarell,"Helvetica Neue",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji"; font-size: inherit;
}
</style>
</head>
<body style="font-size: inherit; -webkit-text-shadow: rgba(255,255,255,.01) 0 0 1px; font-family: "GitLab Sans",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Noto Sans",Ubuntu,Cantarell,"Helvetica Neue",sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";">
<div class="content">
<p style="color: #777777;">
<a href="https://gitlab.rtems.org/opticron">Kinsey Moore</a>
commented on a
discussion on <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/954#note_141723">cpukit/posix/src/aio_suspend.c</a>:
</p>
<table class="code gl-mb-5" style="border-spacing: 0; margin-bottom: 1rem; border-collapse: collapse; width: auto; font-family: monospace; font-size: 90%;" bgcolor="#ffffff" width="100%" cellpadding="0" cellspacing="0">
<tr class="line_holder" style="line-height: 1.6;">
<td class="old_line diff-line-num" data-linenumber="128" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
128
</td>
<td class="new_line diff-line-num" data-linenumber="128" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
128
</td>
<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">suspendcbp</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333333;">requests_left</span><span class="o" style="font-weight: 600;">++</span><span class="p">;</span></span>
</pre></td>
</tr>
<tr class="line_holder" style="line-height: 1.6;">
<td class="old_line diff-line-num" data-linenumber="129" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
129
</td>
<td class="new_line diff-line-num" data-linenumber="129" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
129
</td>
<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"></span>
</pre></td>
</tr>
<tr class="line_holder" style="line-height: 1.6;">
<td class="old_line diff-line-num" data-linenumber="130" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
130
</td>
<td class="new_line diff-line-num" data-linenumber="130" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
130
</td>
<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="p">}</span> <span class="k" style="font-weight: 600;">else</span> <span class="p">{</span></span>
</pre></td>
</tr>
<tr class="line_holder new" style="line-height: 1.6;">
<td class="old_line diff-line-num new" data-linenumber="131" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
</td>
<td class="new_line diff-line-num new" data-linenumber="131" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
131
</td>
<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;">+<span class="line" data-lang="c"> <span class="n" style="color: #333333;">pthread_mutex_unlock</span><span class="p">(</span> <span class="o" style="font-weight: 600;">&</span><span class="n" style="color: #333333;">aio_request_queue</span><span class="p">.</span><span class="n" style="color: #333333;">mutex</span> <span class="p">);</span></span>
</pre></td>
</tr>
<tr class="line_holder" style="line-height: 1.6;">
<td class="old_line diff-line-num" data-linenumber="131" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
131
</td>
<td class="new_line diff-line-num" data-linenumber="132" style="width: 35px; color: rgba(5,5,6,.24); border-right-width: 1px; border-right-color: #ececef; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fbfafd">
132
</td>
<td class="line_content" style="padding: inherit;"><pre style="display: block; font-size: 14px; color: #3a383f; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dcdcde;"> <span class="line" data-lang="c"> <span class="n" style="color: #333333;">pthread_mutex_lock</span><span class="p">(</span> <span class="o" style="font-weight: 600;">&</span><span class="n" style="color: #333333;">request</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333333;">suspendcbp</span><span class="o" style="font-weight: 600;">-></span><span class="n" style="color: #333333;">mutex</span> <span class="p">);</span></span>
</pre></td>
</tr>
</table>
<div class="md" style="position: relative; z-index: 1; color: #3a383f; word-wrap: break-word;">
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Right, resolving a deadlock is typically accomplished by enforcing a strict locking order or a reduction in locking to avoid multiple locks being held at once.</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">Where is the inverse of the locking order that requires this order to be switched/avoided?</p>
<p dir="auto" style="color: #3a383f; margin: 0 0 1rem;" align="initial">The queue is locked because this code is iterating over the items in the queue and this request code is inside the loop that is performing the iteration. It is most certainly not safe to unlock the queue while the iteration is occurring because a modification of the queue during iteration could result in unexpected behavior such as running over the end of the queue if an item is removed while the lock is dropped or missing an item if one is added while the lock is dropped.</p>
<p dir="auto" style="color: #3a383f; margin: 0;" align="initial">The validity of the request object is not in question as it is in the queue and cannot be removed while the queue is locked (assuming code elsewhere cannot destroy a request while it is still in the queue).</p>
</div>
</div>
<div class="footer" style="margin-top: 10px;">
<p style="font-size: small; color: #626168;">
—
<br>
<a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/954#note_141723">View it on GitLab</a>.
<br>
You're receiving this email because of your account on <a target="_blank" rel="noopener noreferrer" href="https://gitlab.rtems.org">gitlab.rtems.org</a>. <a href="https://gitlab.rtems.org/-/sent_notifications/2-adtzc1bm2lyga5ojwy4izxb41/unsubscribe" target="_blank" rel="noopener noreferrer">Unsubscribe</a> from this thread · <a href="https://gitlab.rtems.org/-/profile/notifications" target="_blank" rel="noopener noreferrer" class="mng-notif-link">Manage all notifications</a> · <a href="https://gitlab.rtems.org/help" target="_blank" rel="noopener noreferrer" class="help-link">Help</a>
<span style="color: transparent; font-size: 0; display: none; overflow: hidden; opacity: 0; width: 0; height: 0; max-width: 0; max-height: 0;">
Notification message regarding https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/954#note_141723 at 1770312085
</span>
<script type="application/ld+json">{"@context":"http://schema.org","@type":"EmailMessage","action":{"@type":"ViewAction","name":"View Merge request","url":"https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/954#note_141723"}}</script>
</p>
</div>
</body>
</html>