kernel - Fix TDF_EXITING bug, instrument potential live loops
* Fix a TDF_EXITING bug. lwkt_switch_return() is called to fixup
the 'previous' thread, meaning turning off TDF_RUNNING and handling
TDF_EXITING.
However, if TDF_EXITING is not set, the old thread can be used or
acted upon / exited on by some other cpu the instant we clear
TDF_RUNNING. In this situation it is possible that the other cpu
will set TDF_EXITING in the small window of opportunity just before
we check ourselves, leading to serious thread management corruption.
* The new pmap_inval*() code runs on Xinvltlb instead of as a IPIQ
and can easily create significant latency between the two tests,
whereas the old code ran as an IPIQ and could not due to the critical
section.
tuxillo's projects / dragonfly.git / commit