race where a thread could assume that a process was swapped in by
PHOLD() when it actually wasn't fully swapped in yet.
- In faultin(), always msleep() if PS_SWAPPINGIN is set instead of doing
this check after bumping p_lock in the PS_INMEM == 0 case. Also,
sched_lock is only needed for setting and clearning swapping PS_*
flags and the swap thread inhibitor.
- Don't set and clear the thread swap inhibitor in the same loops as the
pmap_swapin/out_thread() since we have to do it under sched_lock.
Instead, mimic the treatment of the PS_INMEM flag and use separate loops
to set the inhibitors when clearing PS_INMEM and clear the inhibitors
when setting PS_INMEM.
- swapout() now returns with the proc lock held as it holds the lock
while adjusting the swapping-related PS_* flags so that the proc lock
can be used to test those flags.
- Only use the proc lock to check the swapping-related PS_* flags in
several places.
- faultin() no longer requires sched_lock to be held by callers.
- Rename PS_SWAPPING to PS_SWAPPINGOUT to be less ambiguous now that we
have PS_SWAPPINGIN.
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