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Eugene, destroy_context(..) can be called from other place outside of
the scheduler and switch_mm(...). See mmdrop(...) for example.<br>
In many of those cases, the task will run with preemption enable. <br>
<br>
Guillaume.<br>
<br>
<br>
Eugene Surovegin wrote:<br>
<blockquote type="cite"
cite="mid20050712163921.GE25918@gate.ebshome.net">
<pre wrap="">On Tue, Jul 12, 2005 at 10:23:51AM -0400, Guillaume Autran wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Fix for a race condition when a task gets preempted by another task
while executing the destroy_context(...) in a FEW_CONTEXTS environment.
mm->context == NO_CONTEXT but the context_map may indicate all contexts
are in use.
The solution to this problem is to disable kernel preemption while
destroying a MMU context.
Signed-off-by: Guillaume Autran <a class="moz-txt-link-rfc2396E" href="mailto:gautran@mrv.com"><gautran@mrv.com></a>
---
diff -Nru a/include/asm-ppc/mmu_context.h b/include/asm-ppc/mmu_context.h
--- a/include/asm-ppc/mmu_context.h 2005-06-17 15:48:29.000000000 -0400
+++ b/include/asm-ppc/mmu_context.h 2005-07-05 08:58:46.000000000 -0400
@@ -149,6 +149,7 @@
*/
static inline void destroy_context(struct mm_struct *mm)
{
+ preempt_disable();
if (mm->context != NO_CONTEXT) {
clear_bit(mm->context, context_map);
mm->context = NO_CONTEXT;
@@ -156,6 +157,7 @@
atomic_inc(&nr_free_contexts);
#endif
}
+ preempt_enable();
}
static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
</pre>
</blockquote>
<pre wrap=""><!---->
Could you explain, why this patch is needed?
AFAIK, destroy_context() is only called from switch_mm(), which in
turn is called from schedule() with preemption already disabled. If
not, IMHO we have bigger problems, and "fixing" destroy_context() will
only hide such problems.
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="80">--
=======================================
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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