RE: [patch] sched: unlocked context-switches

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>tested on x86, and all other arches should work as well, but if an 
>architecture has irqs-off assumptions in its switch_to() logic 
>it might break. (I havent found any but there may such assumptions.)

The ia64_switch_to() code includes a section that can change a pinned
MMU mapping (when the stack for the new process is in a different
granule from the stack for the old process).  The code beyond the ".map"
label in arch/ia64/kernel/entry.S includes the comment:

.map:
        rsm psr.ic                      // interrupts (psr.i) are already disabled here

I don't think that it would be sufficient to merely add psr.i to this rsm
(and to the ssm 15 lines above).  That would leave a window where we could
take an interrupt, but not be sure that the current stack is pinned.

-Tony
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