Compromise for critical*()/cpu_critical*() recommit. Cleanup the interrupt

disablement assumptions in kern_fork.c by adding another API call,
cpu_critical_fork_exit().  Cleanup the td_savecrit field by moving it
from MI to MD.  Temporarily move cpu_critical*() from <arch>/include/cpufunc.h
to <arch>/<arch>/critical.c (stage-2 will clean this up).

Implement interrupt deferral for i386 that allows interrupts to remain
enabled inside critical sections.  This also fixes an IPI interlock bug,
and requires uses of icu_lock to be enclosed in a true interrupt disablement.

This is the stage-1 commit.  Stage-2 will occur after stage-1 has stabilized,
and will move cpu_critical*() into its own header file(s) + other things.
This commit may break non-i386 architectures in trivial ways.  This should
be temporary.

Reviewed by:	core
Approved by:	core

1 files changed, 4 insertions, 3 deletions

diff --git a/sys/kern/kern_switch.c b/sys/kern/kern_switch.c
index 78505a3..ccfb114 100644
--- a/sys/kern/kern_switch.c
+++ b/sys/kern/kern_switch.c
@@ -77,7 +77,7 @@ critical_enter(void)
 
 	td = curthread;
 	if (td->td_critnest == 0)
-		td->td_savecrit = cpu_critical_enter();
+		cpu_critical_enter();
 	td->td_critnest++;
 }
 
@@ -89,9 +89,10 @@ critical_exit(void)
 	td = curthread;
 	if (td->td_critnest == 1) {
 		td->td_critnest = 0;
-		cpu_critical_exit(td->td_savecrit);
-	} else
+		cpu_critical_exit();
+	} else {
 		td->td_critnest--;
+	}
 }
 
 /*