[src/sommerfeld_i386mp_1]: src/sys/arch/i386/i386 Move call to sched_unlock_i...

[sommerfeld <sommerfeld%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/340cb06b8412
branches:  sommerfeld_i386mp_1
changeset: 482520:340cb06b8412
user:      sommerfeld <sommerfeld%NetBSD.org@localhost>
date:      Tue Apr 30 14:15:14 2002 +0000

description:
Move call to sched_unlock_idle to later in the context switch to
eliminate a race where another processor could grab the outgoing
process before we were done saving our state into it, with predictable
results.

Bug spotted by Frank van der Linden <fvdl%wasabisystems.com@localhost>

Along for the ride:
        clean up register use during switch-to-idle.
        clean up comments regarding register use during context switch.

diffstat:

 sys/arch/i386/i386/locore.s |  30 ++++++++++++++++--------------
 1 files changed, 16 insertions(+), 14 deletions(-)

diffs (102 lines):

diff -r 82cc7382124c -r 340cb06b8412 sys/arch/i386/i386/locore.s
--- a/sys/arch/i386/i386/locore.s       Tue Apr 30 14:09:07 2002 +0000
+++ b/sys/arch/i386/i386/locore.s       Tue Apr 30 14:15:14 2002 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: locore.s,v 1.215.2.31 2002/04/27 20:24:46 sommerfeld Exp $     */
+/*     $NetBSD: locore.s,v 1.215.2.32 2002/04/30 14:15:14 sommerfeld Exp $     */
 
 /*-
  * Copyright (c) 1998, 2000 The NetBSD Foundation, Inc.
@@ -1894,7 +1894,7 @@
         * Registers:
         *   %eax, %ecx - scratch
         *   %esi - old process, then old pcb
-        *   %edi - new process
+        *   %edi - idle pcb
         */
 
        pushl   %esi
@@ -1910,10 +1910,10 @@
        /* Find idle PCB for this CPU */
 #ifndef MULTIPROCESSOR
        movl    $_C_LABEL(proc0),%ebx
-       movl    P_ADDR(%ebx),%esi
+       movl    P_ADDR(%ebx),%edi
        movl    P_MD_TSS_SEL(%ebx),%edx
 #else
-       movl    CPUVAR(IDLE_PCB),%esi
+       movl    CPUVAR(IDLE_PCB),%edi
        movl    CPUVAR(IDLE_TSS_SEL),%edx
 #endif
        movl    $0,CPUVAR(CURPROC)              /* In case we fault... */
@@ -1922,12 +1922,12 @@
        cli
 
        /* Restore stack pointers. */
-       movl    PCB_ESP(%esi),%esp
-       movl    PCB_EBP(%esi),%ebp
+       movl    PCB_ESP(%edi),%esp
+       movl    PCB_EBP(%edi),%ebp
 
 
        /* Switch address space. */
-       movl    PCB_CR3(%esi),%ecx
+       movl    PCB_CR3(%edi),%ecx
        movl    %ecx,%cr3
 
        /* Switch TSS. Reset "task busy" flag before loading. */
@@ -1942,11 +1942,11 @@
        /* We're always in the kernel, so we don't need the LDT. */
 
        /* Restore cr0 (including FPU state). */
-       movl    PCB_CR0(%esi),%ecx
+       movl    PCB_CR0(%edi),%ecx
        movl    %ecx,%cr0
 
        /* Record new pcb. */
-       SET_CURPCB(%esi)
+       SET_CURPCB(%edi)
 
        xorl    %esi,%esi
        sti
@@ -2026,10 +2026,6 @@
        movb    $SONPROC,P_STAT(%edi)   # p->p_stat = SONPROC
        SET_CURPROC(%edi,%ecx)
 
-#if defined(MULTIPROCESSOR) || defined(LOCKDEBUG)      
-       call    _C_LABEL(sched_unlock_idle)
-#endif
-
        /* Skip context switch if same process. */
        cmpl    %edi,%esi
        je      switch_return
@@ -2062,7 +2058,7 @@
         * Third phase: restore saved context.
         *
         * Registers:
-        *   %eax, %ecx, %edx - scratch
+        *   %eax, %ebx, %ecx, %edx - scratch
         *   %esi - new pcb
         *   %edi - new process
         */
@@ -2097,7 +2093,9 @@
        call    _C_LABEL(pmap_activate)         # pmap_activate(p)
        addl    $4,%esp
 
+#if 0
 switch_restored:
+#endif
        /* Restore cr0 (including FPU state). */
        movl    PCB_CR0(%esi),%ecx
 #ifdef MULTIPROCESSOR
@@ -2120,6 +2118,10 @@
        sti
 
 switch_return:
+#if defined(MULTIPROCESSOR) || defined(LOCKDEBUG)      
+       call    _C_LABEL(sched_unlock_idle)
+#endif
+       
        movl    $0,CPL                  # spl0()
        call    _C_LABEL(Xspllower)     # process pending interrupts
        movl    $IPL_HIGH,CPL           # splhigh()