hi,

> Right now the only idea I have is normal sleeping (no upcalls) on page faults.
> 
> Perhaps by stealing the PC trick from restartable atomic sequences we can
> limit disabling upcalls to the thread being active in libpthread ?
> ( Requires some ugly linking tricks to combine object files ? )
> 
> Any ideas on how to solve these problems would be appreciated.

how about a user-kernel shared variable used to indicate if
any upcall handler is executing or not?
(iirc, freebsd kse does a similar thing)

YAMAMOTO Takashi