interrupt stacks

[Anton Blanchard]

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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