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Sorry for the late reply. I was away for the long weekend. However, my
validation test ran all the way through the long weekend ! So, we can
consider this a fix.<br>
See the patch attached.<br>
<br>
Thanks,<br>
Guillaume.<br>
<br>
<br>
Guillaume Autran wrote:<br>
<blockquote type="cite" cite="mid42C3F978.2070305@mrv.com">
<title></title>
Well, disabling preemption in the get_mmu_context() does not help
much... <br>
I'm trying to disable preemption only inside destroy_mmu_context() as
suggested.<br>
Will keep you posted.<br>
<br>
Guillaume.<br>
<br>
<br>
<br>
Marcelo Tosatti wrote:<br>
<blockquote type="cite" cite="mid20050629193846.GA4748@logos.cnet">
<pre wrap="">On Thu, Jun 30, 2005 at 09:26:07AM +1000, Benjamin Herrenschmidt wrote:
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">Execution is resumed exactly where it has been interrupted.
</pre>
<blockquote type="cite">
<pre wrap="">The idea behind my patch was to get rid of that nr_free_contexts counter
that is (I thing) redundant with the context_map.
</pre>
</blockquote>
<pre wrap="">Apparently its there to avoid the spinlock exactly on !FEW_CONTEXTS machines.
I suppose that what happens is that get_mmu_context() gets preempted after stealing
a context (so nr_free_contexts = 0), but before setting next_mmu_context to the
next entry
next_mmu_context = (ctx + 1) & LAST_CONTEXT;
</pre>
</blockquote>
<pre wrap="">Ugh ? Can switch_mm() be preempted at all ? Did I miss yet another
"let's open 10 gazillion races for gun" Ingo patch ?
</pre>
</blockquote>
<pre wrap=""><!---->
Doh nope it can't - my bad.
</pre>
<blockquote type="cite">
<blockquote type="cite">
<pre wrap="">So if the now running higher prio tasks calls switch_mm() (which is likely to happen)
it loops forever on atomic_dec_if_positive(&nr_free_contexts), while steal_context()
sees "mm->context == CONTEXT".
</pre>
</blockquote>
<pre wrap="">I think the race is only when destroy_context() is preempted, but maybe
I missed something.
</pre>
</blockquote>
<pre wrap=""><!---->
Nope, I think you are right. My "theory" is obviously flawed now.
There seem to be several contexts where destroy_context() could be called
with preempt enabled - I should have been shutup in the first place :)
Lets wait for Guillaume to test...
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
=======================================
Guillaume Autran
Senior Software Engineer
MRV Communications, Inc.
Tel: (978) 952-4932 office
E-mail: <a class="moz-txt-link-abbreviated"
href="mailto:gautran@mrv.com">gautran@mrv.com</a>
======================================= </pre>
<pre wrap="">
<hr width="90%" size="4">
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
=======================================
Guillaume Autran
Senior Software Engineer
MRV Communications, Inc.
Tel: (978) 952-4932 office
E-mail: <a class="moz-txt-link-abbreviated" href="mailto:gautran@mrv.com">gautran@mrv.com</a>
======================================= </pre>
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