interrupt stacks

[Dave Engebretsen]

It seems that if we are certain no recursion can occur, the stacks
should be removed.  Debugging that problem the first time around was
quite time consuming, so we should be very sure of this fact.

Do you have a patch, or could you just add the code into 2.4 BK to fix
the problems found in xics.c?

Thanks -

Dave.

Anton Blanchard wrote:
>
> Hi,
>
> In 2.4 we have interrupt stacks. It turns out there were a number of
> issues with the xics irq routines, Milton and I weeded them out in 2.5
> over the last few months. There were windows where we could take irqs
> recursively, resulting in excessive stack usage.
>
> In 2.5 interrupt stacks are disabled because the thread_info changes
> broke it. The thread_info by default lives at the bottom of the kernel
> stack, and switching stacks on the fly confuses it greatly.
>
> Our options are:
>
> 1 fix thread_info. Some recent changes pushed by ia64 should allow us to
> move the thread_info into the task_struct.
>
> 2 remove interrupt stacks. We have done very heavy testing of 2.5 in the
> lab and have not seen any stack overflow problems. Now that we cant
> take recursive irqs we shouldnt be able to overflow a tasks stack.
>
> Im leaning towards option 2, if we dont need interrupt stacks then there
> is no need for that complexity. Thoughts?
>
> Anton
>

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