Final word on the locking fiasco?

Change pushcli / popcli so that they can never turn on
interrupts unexpectedly.  That is, if interrupts are on,
then pushcli(); popcli(); turns them off and back on, but
if they are off to begin with, then pushcli(); popcli(); is
a no-op.

I think our fundamental mistake was having a primitive
(release and then popcli nee spllo) that could turn
interrupts on at unexpected moments instead of being
explicit about when we want to start allowing interrupts.

With the new semantics, all the manual fiddling of ncli
to force interrupts off in certain sections goes away.
In return, we must explicitly mark the places where
we want to enable interrupts unconditionally, by calling sti().
There is only one: inside the scheduler loop.

1 files changed, 2 insertions, 2 deletions

diff --git a/proc.h b/proc.h
index 36913c4..fa60452 100644
--- a/proc.h
+++ b/proc.h
@@ -56,9 +56,9 @@ struct cpu {
   struct context context;     // Switch here to enter scheduler
   struct taskstate ts;        // Used by x86 to find stack for interrupt
   struct segdesc gdt[NSEGS];  // x86 global descriptor table
-  char *stack;
   volatile int booted;        // Has the CPU started?
-  int ncli;                 // Depth of pushcli nesting.
+  int ncli;                   // Depth of pushcli nesting.
+  int intena;                 // Were interrupts enabled before pushcli? 
 };
 
 extern struct cpu cpus[NCPU];