Re: kernel: supervisor trap asynchronous system trap, code=0

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Sat, Jun 30, 2007 at 08:09:47PM +0900, YAMAMOTO Takashi wrote:
> > Index: i386/locore.S
> > ===================================================================
> > RCS file: /cvsroot/src/sys/arch/xen/i386/locore.S,v
> > retrieving revision 1.25
> > diff -u -r1.25 locore.S
> > --- i386/locore.S   17 May 2007 14:51:35 -0000      1.25
> > +++ i386/locore.S   28 Jun 2007 13:27:49 -0000
> > @@ -663,6 +663,7 @@
> >      * Switch to newlwp's stack.
> >      */
> >  
> > +   CLI(%ebx)
> >     movl    L_ADDR(%edi),%ebx
> >     movl    PCB_EBP(%ebx),%ebp
> >     movl    PCB_ESP(%ebx),%esp
> 
> can you explain why it's necessary?

I didn't find why an interrupt coming in there would cause problem,
but I can confirm that this prevent the KASSERT panic that was being reported.
Also, I notice that the code in netbsd-4 does the process stack swicthing
with interrupts disabled.

> 
> anyway, please don't call ras_lookup with interrupt disabled.

OK. I just wanted to make sure the new context was fully installed before
re-taking interrupts. I didn't notice a C function was being called.

> 
> > @@ -780,9 +789,29 @@
> >     call    _C_LABEL(trap)
> >     addl    $4,%esp
> >     jmp     .Lsyscall_checkast
> > -1: STI(%eax)
> > -   CHECK_DEFERRED_SWITCH(%eax)
> > +1: CHECK_DEFERRED_SWITCH(%eax)
> >     jnz     9f
> > +   STIC(%eax)
> > +   jz      14f
> > +   call    _C_LABEL(stipending)
> > +   testl   %eax,%eax
> > +   jz      14f
> > +   /* process pending interrupts */
> > +   CLI(%eax)
> > +   movl    CPUVAR(ILEVEL), %ebx
> > +   movl    $.Lsyscall_resume, %esi # address to resume loop at
> > +.Lsyscall_resume:
> > +   movl    %ebx,%eax               # get cpl
> > +   movl    CPUVAR(IUNMASK)(,%eax,4),%eax
> > +   andl    CPUVAR(IPENDING),%eax   # any non-masked bits left?
> > +   jz      17f
> > +   bsrl    %eax,%eax
> > +   btrl    %eax,CPUVAR(IPENDING)
> > +   movl    CPUVAR(ISOURCES)(,%eax,4),%eax
> > +   jmp     *IS_RESUME(%eax)
> > +17:        movl    %ebx, CPUVAR(ILEVEL)    #restore cpl
> > +   jmp     .Lsyscall_checkast
> > +14:
> >  #ifndef DIAGNOSTIC
> >     INTRFASTEXIT
> >  #else /* DIAGNOSTIC */
> 
> can't these duplicated code be shared?

it could probably, but this would make some more call/return, or jump.
I'm not sure it's worth it.

> 
> i'm not sure why stipending() was needed in the first place,
> in addition to __sti() and do_hypervisor_callback().

__sti() is intended for C code, but it takes an extrat trap and 4 context
switches to process pending interrupts. processing interrupts in the current
context it more efficient.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--