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From: bugzilla@dpdk.org
To: dev@dpdk.org
Subject: [DPDK/core Bug 1385] rt_bitops.h fails to give implied atomicity
guarantees
Date: Mon, 26 Feb 2024 09:56:53 +0000
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Date: Mon, 26 Feb 2024 10:56:53 +0100
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https://bugs.dpdk.org/show_bug.cgi?id=3D1385
Bug ID: 1385
Summary: rt_bitops.h fails to give implied atomicity guarantees
Product: DPDK
Version: 23.11
Hardware: All
OS: All
Status: UNCONFIRMED
Severity: normal
Priority: Normal
Component: core
Assignee: dev@dpdk.org
Reporter: mattias.ronnblom@ericsson.com
Target Milestone: ---
The documentation (and the naming) for the rte_bit_relaxed_*() functions in
rte_bitops.h makes clear that all such functions have a relaxed memory orde=
r.
The use of the term "relaxed", which most C programmers likely are familiar
with from the C11 memory model specification, itself implies that the
operations are supposed to be atomic. Why otherwise mention the memory
operations are relaxed? Relaxed is the default for non-atomic loads and sto=
res.
In addition, why otherwise declare the address as volatile?
An even stronger indication are the test-and-set family of "relaxed"
rte_bitops.h functions. "Test-and-set" in the low-level C programming conte=
xt
always implies an atomic operation. A non-atomic test-and-set does not make
sense.
In summary, a perfectly valid interpretation of the API contract is that the
functions are atomic.
However, their implementation is not, which may not be obvious to the causal
API user.
--=20
You are receiving this mail because:
You are the assignee for the bug.=
--17089414130.60ae2.2504000
Date: Mon, 26 Feb 2024 10:56:53 +0100
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<html>
<head>
<base href=3D"https://bugs.dpdk.org/">
</head>
<body><table border=3D"1" cellspacing=3D"0" cellpadding=3D"8" class=3D"=
bz_new_table">
<tr>
<th>Bug ID</th>
<td><a class=3D"bz_bug_link=20
bz_status_UNCONFIRMED "
title=3D"UNCONFIRMED - rt_bitops.h fails to give implied atomicity guara=
ntees"
href=3D"https://bugs.dpdk.org/show_bug.cgi?id=3D1385">1385</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>rt_bitops.h fails to give implied atomicity guarantees
</td>
</tr>
<tr>
<th>Product</th>
<td>DPDK
</td>
</tr>
<tr>
<th>Version</th>
<td>23.11
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>UNCONFIRMED
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>Normal
</td>
</tr>
<tr>
<th>Component</th>
<td>core
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dev@dpdk.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mattias.ronnblom@ericsson.com
</td>
</tr>
<tr>
<th>Target Milestone</th>
<td>---
</td>
</tr></table>
<p>
<div class=3D"bz_comment_block">
<pre class=3D"bz_comment_text">The documentation (and the naming)=
for the rte_bit_relaxed_*() functions in
rte_bitops.h makes clear that all such functions have a relaxed memory orde=
r.
The use of the term "relaxed", which most C programmers likely ar=
e familiar
with from the C11 memory model specification, itself implies that the
operations are supposed to be atomic. Why otherwise mention the memory
operations are relaxed? Relaxed is the default for non-atomic loads and sto=
res.
In addition, why otherwise declare the address as volatile?
An even stronger indication are the test-and-set family of "relaxed&qu=
ot;
rte_bitops.h functions. "Test-and-set" in the low-level C program=
ming context
always implies an atomic operation. A non-atomic test-and-set does not make
sense.
In summary, a perfectly valid interpretation of the API contract is that the
functions are atomic.
However, their implementation is not, which may not be obvious to the causal
API user.
</pre>
</div>
</p>
<hr>
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