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Re: Hitachi djprobe mechanism
* Andi Kleen (ak@suse.de) wrote:
> On Wed, Aug 03, 2005 at 08:26:56PM -0400, Mathieu Desnoyers wrote:
> > * Roland McGrath (roland@redhat.com) wrote:
> > > It's OK for probe insertion to be slow. So why not use RCU to synchronize
> > > other processors?
> > >
> >
> > No,
> >
> > The reason is we have no control on preemption disabling around the concerned
> > area.
>
> Task list walking and checking of the IP of blocked processes can avoid that
> as earlier discussed. But it doesn't solve all problems with short instructions.
> IPI is the most practical one.
>
>
No practical solution has been elaborated for a fully preemptible kernel. Even
walking on the talk list checking for potential iret pointers is not a good
idea: If you have a stopped process that has its instruction pointer exactly in
the wrong area, then you may wait forever.
Per cpu workqueue to make sure none is still in interrupt context would, I
think, do the same as a non maskable IPI but without the busy looping.
Mathieu
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