[PATCH] 8xx: get_mmu_context() for (very) FEW_CONTEXTS and KERNEL_PREEMPT race/starvation issue

[Guillaume Autran]

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.

Guillaume.

-- 
=======================================
Guillaume Autran
Senior Software Engineer
MRV Communications, Inc.
Tel: (978) 952-4932 office
E-mail: gautran at mrv.com
======================================= 

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