Merge td_epochnest with td_no_sleeping.

Epoch itself doesn't rely on the counter and it is provided
merely for sleeping subsystems to check it.

- In functions that sleep use THREAD_CAN_SLEEP() to assert
  correctness.  With EPOCH_TRACE compiled print epoch info.
- _sleep() was a wrong place to put the assertion for epoch,
  right place is sleepq_add(), as there ways to call the
  latter bypassing _sleep().
- Do not increase td_no_sleeping in non-preemptible epochs.
  The critical section would trigger all possible safeguards,
  no sleeping counter is extraneous.

Reviewed by:	kib

1 files changed, 6 insertions, 8 deletions

diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
index 88abc78085c4..6a73f700e12e 100644
--- a/sys/kern/subr_trap.c
+++ b/sys/kern/subr_trap.c
@@ -166,12 +166,6 @@ userret(struct thread *td, struct trapframe *frame)
 	WITNESS_WARN(WARN_PANIC, NULL, "userret: returning");
 	KASSERT(td->td_critnest == 0,
 	    ("userret: Returning in a critical section"));
-#ifdef EPOCH_TRACE
-	if (__predict_false(curthread->td_epochnest > 0))
-		epoch_trace_list(curthread);
-#endif
-	KASSERT(td->td_epochnest == 0,
-	    ("userret: Returning in an epoch section"));
 	KASSERT(td->td_locks == 0,
 	    ("userret: Returning with %d locks held", td->td_locks));
 	KASSERT(td->td_rw_rlocks == 0,
@@ -185,8 +179,12 @@ userret(struct thread *td, struct trapframe *frame)
 	    td->td_lk_slocks));
 	KASSERT((td->td_pflags & TDP_NOFAULTING) == 0,
 	    ("userret: Returning with pagefaults disabled"));
-	KASSERT(THREAD_CAN_SLEEP(),
-	    ("userret: Returning with sleep disabled"));
+	if (__predict_false(!THREAD_CAN_SLEEP())) {
+#ifdef EPOCH_TRACE
+		epoch_trace_list(curthread);
+#endif
+		KASSERT(1, ("userret: Returning with sleep disabled"));
+	}
 	KASSERT(td->td_pinned == 0 || (td->td_pflags & TDP_CALLCHAIN) != 0,
 	    ("userret: Returning with with pinned thread"));
 	KASSERT(td->td_vp_reserv == 0,