There are risks associated with waiting on a preemptible epoch section.
Change the name to make them not be the default and document the issue
under CAVEATS.
Reported by: markj
adds:
- epoch_enter_critical() - can be called inside a different epoch,
starts a section that will acquire any MTX_DEF mutexes or do
anything that might sleep.
- epoch_exit_critical() - corresponding exit call
- epoch_wait_critical() - wait variant that is guaranteed that any
threads in a section are running.
- epoch_global_critical - an epoch_wait_critical safe epoch instance
Requested by: markj
Approved by: sbruno
Read locking is over used in the kernel to guarantee liveness. This API makes
it easy to provide livenes guarantees without atomics.
Includes epoch_test kernel module to stress test the API.
Documentation will follow initial use case.
Test case and improvements to preemption handling in response to discussion
with mjg@
Reviewed by: imp@, shurd@
Approved by: sbruno@
