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<title>Fix nv_drm_revoke_modeset_permission</title>
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<header id="title-block-header">
<h1 class="title">Fix nv_drm_revoke_modeset_permission</h1>
</header>
<h1 id="fix-nv_drm_revoke_modeset_permission-kernel-warning">Fix:
<code>nv_drm_revoke_modeset_permission</code> kernel WARNING</h1>
<p>Fixes a kernel <code>WARN_ON</code> in
<code>nv_drm_revoke_modeset_permission</code> on the nvidia-drm 550
branch with Debian kernel 6.12. The warning fires every time a DRM file
descriptor is closed (by processes like <code>glxtest</code>,
<code>kioworker</code>, <code>kscreenlocker_greet</code>),
producing:</p>
<pre><code>WARNING at nvidia-drm/nvidia-drm-drv.c:1221 nv_drm_revoke_modeset_permission+0x327/0x340</code></pre>
<p>Two patches are needed: one fixing a conftest compile failure
(primary cause) and one fixing latent error-handling bugs in the
driver.</p>
<h2 id="files">Files</h2>
<table>
<colgroup>
<col style="width: 31%" />
<col style="width: 68%" />
</colgroup>
<thead>
<tr>
<th>File</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td><a href="plan.md">plan.md</a></td>
<td>Full root-cause analysis with source references to NVIDIA and kernel
code. Covers the conftest failure, the bogus <code>WARN_ON</code> in the
fallback macro, the wrong mutex assertion for atomic drivers, and two
secondary bugs (iterator leak, NULL state dereference). Start here to
understand the problem.</td>
</tr>
<tr>
<td><a href="plan.html">plan.html</a></td>
<td>HTML rendering of <code>plan.md</code> (generated via pandoc). Same
content with clickable hyperlinks, suitable for viewing in a
browser.</td>
</tr>
<tr>
<td><a
href="nvidia-graphics-drivers-550-debian-sources.patch">nvidia-graphics-drivers-550-debian-sources.patch</a></td>
<td>Git-format patch against the <a
href="https://salsa.debian.org/nvidia-team/nvidia-graphics-drivers">Debian
nvidia-graphics-drivers</a> source package. Contains both fix patches
(0084 + 0085), updates to <code>debian/patches/module/series</code>, and
a changelog entry. Apply this to build a fixed <code>.deb</code>.</td>
</tr>
<tr>
<td><a href="conftest.sh.patched">conftest.sh.patched</a></td>
<td>The full <code>conftest.sh</code> from
<code>kernel-open/conftest.sh</code> (tag 550.163.01) with the fix
already applied: prerequisite DRM headers (<code>drm_device.h</code>,
<code>drm_mode_config.h</code>) are included before
<code>drm_connector.h</code>, and a <code>return 0;</code> is added to
avoid <code>-Werror=return-type</code>.</td>
</tr>
<tr>
<td><a href="nvidia-drm-drv.c.patched">nvidia-drm-drv.c.patched</a></td>
<td>The full <code>kernel-open/nvidia-drm/nvidia-drm-drv.c</code> (tag
550.163.01) with error-handling fixes applied: <code>goto done</code>
replaced with <code>break</code> in the connector loop, explicit error
check after iterator end, and NULL guards on
<code>drm_atomic_state_put</code>/<code>drm_atomic_state_free</code>.</td>
</tr>
</tbody>
</table>
<h2 id="how-to-use">How to use</h2>
<h3 id="option-a-patch-dkms-sources-directly">Option A: Patch DKMS
sources directly</h3>
<p>Back up the original files first, then copy the patched versions into
the DKMS source tree and rebuild:</p>
<div class="sourceCode" id="cb2"><pre
class="sourceCode bash"><code class="sourceCode bash"><span id="cb2-1"><a href="#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="fu">sudo</span> <span class="at">-s</span></span>
<span id="cb2-2"><a href="#cb2-2" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-3"><a href="#cb2-3" aria-hidden="true" tabindex="-1"></a><span class="co"># Copy patched files to the DKMS source tree</span></span>
<span id="cb2-4"><a href="#cb2-4" aria-hidden="true" tabindex="-1"></a><span class="fu">cp</span> <span class="at">-v</span> conftest.sh.patched /usr/src/nvidia-current-550.163.01/</span>
<span id="cb2-5"><a href="#cb2-5" aria-hidden="true" tabindex="-1"></a><span class="fu">cp</span> <span class="at">-v</span> nvidia-drm-drv.c.patched /usr/src/nvidia-current-550.163.01/nvidia-drm/</span>
<span id="cb2-6"><a href="#cb2-6" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-7"><a href="#cb2-7" aria-hidden="true" tabindex="-1"></a><span class="bu">cd</span> /usr/src/nvidia-current-550.163.01</span>
<span id="cb2-8"><a href="#cb2-8" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-9"><a href="#cb2-9" aria-hidden="true" tabindex="-1"></a><span class="co"># Back up originals</span></span>
<span id="cb2-10"><a href="#cb2-10" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> conftest.sh conftest.sh.orig</span>
<span id="cb2-11"><a href="#cb2-11" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> nvidia-drm/nvidia-drm-drv.c nvidia-drm/nvidia-drm-drv.c.orig</span>
<span id="cb2-12"><a href="#cb2-12" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-13"><a href="#cb2-13" aria-hidden="true" tabindex="-1"></a><span class="co"># Put patched files in place (-i prompts before overwriting)</span></span>
<span id="cb2-14"><a href="#cb2-14" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> conftest.sh.patched conftest.sh</span>
<span id="cb2-15"><a href="#cb2-15" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> nvidia-drm/nvidia-drm-drv.c.patched nvidia-drm/nvidia-drm-drv.c</span>
<span id="cb2-16"><a href="#cb2-16" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb2-17"><a href="#cb2-17" aria-hidden="true" tabindex="-1"></a><span class="co"># Rebuild the DKMS module</span></span>
<span id="cb2-18"><a href="#cb2-18" aria-hidden="true" tabindex="-1"></a><span class="ex">dkms</span> remove nvidia-current/550.163.01 <span class="at">--all</span></span>
<span id="cb2-19"><a href="#cb2-19" aria-hidden="true" tabindex="-1"></a><span class="ex">dkms</span> install nvidia-current/550.163.01</span>
<span id="cb2-20"><a href="#cb2-20" aria-hidden="true" tabindex="-1"></a><span class="ex">update-initramfs</span> <span class="at">-u</span> <span class="co"># or: dracut -f</span></span>
<span id="cb2-21"><a href="#cb2-21" aria-hidden="true" tabindex="-1"></a><span class="ex">reboot</span></span></code></pre></div>
<p>To revert, restore the backups:</p>
<div class="sourceCode" id="cb3"><pre
class="sourceCode bash"><code class="sourceCode bash"><span id="cb3-1"><a href="#cb3-1" aria-hidden="true" tabindex="-1"></a><span class="fu">sudo</span> <span class="at">-s</span></span>
<span id="cb3-2"><a href="#cb3-2" aria-hidden="true" tabindex="-1"></a><span class="bu">cd</span> /usr/src/nvidia-current-550.163.01</span>
<span id="cb3-3"><a href="#cb3-3" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> conftest.sh.orig conftest.sh</span>
<span id="cb3-4"><a href="#cb3-4" aria-hidden="true" tabindex="-1"></a><span class="fu">mv</span> <span class="at">-i</span> nvidia-drm/nvidia-drm-drv.c.orig nvidia-drm/nvidia-drm-drv.c</span>
<span id="cb3-5"><a href="#cb3-5" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb3-6"><a href="#cb3-6" aria-hidden="true" tabindex="-1"></a><span class="co"># Rebuild the DKMS module</span></span>
<span id="cb3-7"><a href="#cb3-7" aria-hidden="true" tabindex="-1"></a><span class="ex">dkms</span> remove nvidia-current/550.163.01 <span class="at">--all</span></span>
<span id="cb3-8"><a href="#cb3-8" aria-hidden="true" tabindex="-1"></a><span class="ex">dkms</span> install nvidia-current/550.163.01</span>
<span id="cb3-9"><a href="#cb3-9" aria-hidden="true" tabindex="-1"></a><span class="ex">update-initramfs</span> <span class="at">-u</span> <span class="co"># or: dracut -f</span></span>
<span id="cb3-10"><a href="#cb3-10" aria-hidden="true" tabindex="-1"></a><span class="ex">reboot</span></span></code></pre></div>
<h3 id="option-b-apply-the-debian-source-patch">Option B: Apply the
Debian source patch</h3>
<p>If you maintain a local build of the Debian
<code>nvidia-graphics-drivers</code> package:</p>
<div class="sourceCode" id="cb4"><pre
class="sourceCode bash"><code class="sourceCode bash"><span id="cb4-1"><a href="#cb4-1" aria-hidden="true" tabindex="-1"></a><span class="bu">cd</span> nvidia-graphics-drivers</span>
<span id="cb4-2"><a href="#cb4-2" aria-hidden="true" tabindex="-1"></a><span class="fu">git</span> am nvidia-graphics-drivers-550-debian-sources.patch</span>
<span id="cb4-3"><a href="#cb4-3" aria-hidden="true" tabindex="-1"></a><span class="ex">dpkg-buildpackage</span> <span class="at">-us</span> <span class="at">-uc</span></span></code></pre></div>
<h3 id="verification">Verification</h3>
<p>After rebooting with the patched module:</p>
<div class="sourceCode" id="cb5"><pre
class="sourceCode bash"><code class="sourceCode bash"><span id="cb5-1"><a href="#cb5-1" aria-hidden="true" tabindex="-1"></a><span class="co"># Conftest should now detect the struct:</span></span>
<span id="cb5-2"><a href="#cb5-2" aria-hidden="true" tabindex="-1"></a><span class="fu">grep</span> NV_DRM_CONNECTOR_LIST_ITER /var/lib/dkms/nvidia-current/550.163.01/build/conftest/types.h</span>
<span id="cb5-3"><a href="#cb5-3" aria-hidden="true" tabindex="-1"></a><span class="co"># Expected: #define NV_DRM_CONNECTOR_LIST_ITER_PRESENT</span></span>
<span id="cb5-4"><a href="#cb5-4" aria-hidden="true" tabindex="-1"></a></span>
<span id="cb5-5"><a href="#cb5-5" aria-hidden="true" tabindex="-1"></a><span class="co"># </span><span class="al">WARNING</span><span class="co"> should no longer appear:</span></span>
<span id="cb5-6"><a href="#cb5-6" aria-hidden="true" tabindex="-1"></a><span class="fu">dmesg</span> <span class="kw">|</span> <span class="fu">grep</span> nv_drm_revoke_modeset_permission</span>
<span id="cb5-7"><a href="#cb5-7" aria-hidden="true" tabindex="-1"></a><span class="co"># Expected: no output</span></span></code></pre></div>
<hr />
<p><em>Analysis and patches created with assistance from Claude Opus 4.6
(Anthropic) via Cursor IDE.</em></p>
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