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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - DisplayLink (udl) Linux kernel memory fault on USB hot unplug, proposed patch"
href="https://bugs.freedesktop.org/show_bug.cgi?id=89549">89549</a>
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<th>Summary</th>
<td>DisplayLink (udl) Linux kernel memory fault on USB hot unplug, proposed patch
</td>
</tr>
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<th>Product</th>
<td>DRI
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>x86-64 (AMD64)
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<th>OS</th>
<td>Linux (All)
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>medium
</td>
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<th>Component</th>
<td>DRM/other
</td>
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<th>Assignee</th>
<td>dri-devel@lists.freedesktop.org
</td>
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<th>Reporter</th>
<td>adam_richter2004@yahoo.com
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=114235" name="attach_114235" title="Add ".get_vblank_counter = drm_vblank_count," to DisplayLink drm_driver functions">attachment 114235</a> <a href="attachment.cgi?id=114235&action=edit" title="Add ".get_vblank_counter = drm_vblank_count," to DisplayLink drm_driver functions">[details]</a></span>
Add ".get_vblank_counter = drm_vblank_count," to DisplayLink drm_driver
functions
[This is an edit of an email that I sent yesterday to linux-fbdev at
vger.kernel.org and the Linux kernel udlfb maintainer.]
In Linux-4.0-rc3, the DisplayLink driver gets a kernel memory fault when its
USB device is unplugged, specifically when vblank_disable_and_save in
linux-4.0-rc3/drivers/gpu/drm/drm_irq.c attempts to call the NULL function
pointer dev->driver_get_vblank_counter.
linux-4.0-rc3/Documentation/DocBook/drm.tmpl says of that field, "Otherwise
drivers can use the drm_vblank_count helper function to handle this operation."
Trying that seems to have eliminated the oops when I unplug the device,
although I do see these lines in the console log at device driver
initialization time that I think are probably fine, but which I should mention
in case the indicate that I did the wrong the thing:
[drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[drm] No driver support for vblank timestamp query.
If that doesn't look like a problem, then please apply the attached patch and
push it upstream. The patch just adds one line that appears in six other
framebuffer drivers to initialize the driver_get_vblank_counter drm_driver
function.
Thanks in advance for your attention to this problem.</pre>
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