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Benjamin Herrenschmidt wrote:<br>
<blockquote type="cite" cite="mid1120018530.5133.241.camel@gaston">
<pre wrap="">On Tue, 2005-06-28 at 09:42 -0400, Guillaume Autran wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Hi,
I happen to notice a race condition in the mmu_context code for the 8xx
with very few context (16 MMU contexts) and kernel preemption enable. It
is hard to reproduce has it shows only when many processes are
created/destroy and the system is doing a lot of IRQ processing.
In short, one process is trying to steal a context that is in the
process of being freed (mm->context == NO_CONTEXT) but not completely
freed (nr_free_contexts == 0).
The steal_context() function does not do anything and the process stays
in the loop forever.
Anyway, I got a patch that fixes this part. Does not seem to affect
scheduling latency at all.
Comments are appreciated.
</pre>
</blockquote>
<pre wrap=""><!---->
Your patch seems to do a hell lot more than fixing this race ... What
about just calling preempt_disable() in destroy_context() instead ?
</pre>
</blockquote>
I'm still a bit confused with "kernel preemption". One thing for sure
is that disabling kernel preemption does indeed fix my problem.<br>
So, my question is, what if a task in the middle of being schedule gets
preempted by an IRQ handler, where will this task restart execution ?
Back at the beginning of schedule or where it left of ?<br>
<br>
The idea behind my patch was to get rid of that nr_free_contexts
counter that is (I thing) redundant with the context_map.<br>
<br>
Regards,<br>
Guillaume.<br>
<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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