Round out the facilty for a 'bound' thread to loan out its KSE

in specific situations. The owner thread must be blocked, and the
borrower can not proceed back to user space with the borrowed KSE.
The borrower will return the KSE on the next context switch where
teh owner wants it back. This removes a lot of possible
race conditions and deadlocks. It is consceivable that the
borrower should inherit the priority of the owner too.
that's another discussion and would be simple to do.

Also, as part of this, the "preallocatd spare thread" is attached to the
thread doing a syscall rather than the KSE. This removes the need to lock
the scheduler when we want to access it, as it's now "at hand".

DDB now shows a lot mor info for threaded proceses though it may need
some optimisation to squeeze it all back into 80 chars again.
(possible JKH project)

Upcalls are now "bound" threads, but "KSE Lending" now means that
other completing syscalls can be completed using that KSE before the upcall
finally makes it back to the UTS. (getting threads OUT OF THE KERNEL is
one of the highest priorities in the KSE system.) The upcall when it happens
will present all the completed syscalls to the KSE for selection.

1 files changed, 6 insertions, 8 deletions

diff --git a/sys/kern/kern_condvar.c b/sys/kern/kern_condvar.c
index 26f5376..3ce9aff 100644
--- a/sys/kern/kern_condvar.c
+++ b/sys/kern/kern_condvar.c
@@ -130,16 +130,14 @@ cv_check_upcall(struct thread *td)
 	if ((td->td_proc->p_flag & P_KSES) && td->td_mailbox &&
 	    (td->td_flags & TDF_INMSLEEP) == 0) {
 		/*
-		 * If we have no queued work to do,
-		 * upcall to the UTS to see if it has more work.
 		 * We don't need to upcall now, just queue it.
+		 * The upcall will happen when other n-kernel work
+		 * in this SKEGRP has completed.
+		 * Don't recurse here!
 		 */
-		if (TAILQ_FIRST(&td->td_ksegrp->kg_runq) == NULL) {
-			/* Don't recurse here! */
-			td->td_flags |= TDF_INMSLEEP;
-			thread_schedule_upcall(td, td->td_kse);
-			td->td_flags &= ~TDF_INMSLEEP;
-		}
+		td->td_flags |= TDF_INMSLEEP;
+		thread_schedule_upcall(td, td->td_kse);
+		td->td_flags &= ~TDF_INMSLEEP;
 	}
 }