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List:       linux-ia64
Subject:    Re: [PATCH&RFC 2/2] OS_MCA Recovery from poisoned memory read
From:       Christian Cotte-Barrot <Christian.Cotte-Barrot () bull ! net>
Date:       2004-08-23 8:29:20
Message-ID: 4129AAE0.4726DAC8 () bull ! net
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Hidetoshi Seto wrote:
> 
> Keith Owens wrote:
> > mca_handler_bh() is running as an extension of the MCA event which
> > means that it is not irq safe.  It is not safe to get any external lock
> > in mca_page_isolate() or mca_handler_bh().
> 
> Therefore the MCA handler couldn't recover the system if the process is
> running in kernel-mode since it possibly has such important kernel locks.
> 
> > AFAICT, my concerns about the MCA event and mca_handler_bh() not being
> > irq safe are only a problem for the case when the MCA was triggered by
> > user space code but was delivered when the cpu was in kernel code.
> > Maybe we do not support the problem case.
> >
> > *    offending process  affected process  OS MCA do
> > *     kernel mode        kernel mode       down system
> > *     kernel mode        user   mode       kill the process
> > *     user   mode        kernel mode       kill the process <=== problem
> > *     user   mode        user   mode       kill the process
> 
> So we have to guarantee that the process is running in user-mode,
> which all processes can't have any locks of kernel, right?
> 
> It would be happy if this fixed patch satisfy your requirement.
> 

Surprising it looks like a discovery (locking problem within the
mca handler) ?

Here is Zoltan's document including a design that exposes a solution 
how to avoid race (paragraphs 3.5, 3.5.1, 3.5.2 ...) and many other
stuff :
  http://mca-recovery.sourceforge.net
    Linux Itanium MCA Recovery Design Document, third draft
      http://mca-recovery.sourceforge.net/mca3.html

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