Date: Sun, 02 Sep 2001 01:25:00 -0700 From: Peter Wemm <peter@wemm.org> To: Andrew Gallatin <gallatin@cs.duke.edu> Cc: John Baldwin <jhb@FreeBSD.ORG>, freebsd-alpha@FreeBSD.ORG, cvs-committers@FreeBSD.ORG Subject: Re: cvs commit: src/sys/alpha/alpha pmap.c Message-ID: <20010902082500.5A0FD3807@overcee.netplex.com.au> In-Reply-To: <15247.55907.363565.267385@grasshopper.cs.duke.edu>
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Andrew Gallatin wrote:
>
> John Baldwin writes:
> > Can you do a 'l *0xfffffc0000582da8' in gdb to see what source line it die
d on?
>
> 0xfffffc0000582da8 is in pmap_remove_pages (../../../alpha/alpha/pmap.c:2612)
>
> Which ends up being:
>
> 2607 #ifdef PMAP_REMOVE_PAGES_CURPROC_ONLY
> 2608 pte = vtopte(pv->pv_va);
> 2609 #else
> 2610 pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
> 2611 #endif
> 2612 if (!pmap_pte_v(pte))
> 2613 panic("pmap_remove_pages: page on pm_pvlist h
as no pte\n");
> 2614 tpte = *pte;
Well, I'm confused now. I've reread the 1.63 -> 1.64 diff about 50
times now and I cannot for the life of me see any actual real change.
Maybe I've been looking at it for so long now that I cannot see what
is staring right at me? Can you please look over the diff and see
if you can spot something that I cannot see?
Also, do you see an immediate explosion or one at some later point? Is it
repeatable - if not, is it possible that you just had the semi-regular
crash with the -current while running the new kernel?
What is the value of "pte" BTW?
pmap_dispose_proc() is essentially changed like this:
+ vm_offset_t up;
- ptek = vtopte((vm_offset_t) p->p_addr);
+ up = (vm_offset_t)p->p_addr;
+ ptek = vtopte(up);
- if ((m = vm_page_lookup(upobj, i)) == NULL)
+ m = vm_page_lookup(upobj, i);
+ if (m == NULL)
- pmap_invalidate_page(kernel_pmap, (vm_offset_t)p->p_addr + i * PAGE_SIZE);
+ pmap_invalidate_page(kernel_pmap, up + i * PAGE_SIZE);
The rest is whitespace. I really dont see how this can lead to the
kind of crash you saw. :-(
Anyway, the next thing to try is to back out one of the four functions
at a time.. (or do a binary search, backing out 2 then either the 3rd or
restoring 1).
I would look over the asm code but I just *know* gcc is going to produce
totally unrecognizable assembler differences. :-(
There is some serious badness with object / resource management here. When
a process is created, its vm object is created and *never* destroyed. Its
pointer is left in p_upages_obj across exit() and later with a new fork().
It depends on the vm zones being type safe and preserving their contents
across zfree() / zalloc(). At least it releases the pages at exit.
I will rebuild my UP2000 at work and retest it there as well. I'll let you
know what happens.
Cheers,
-Peter
--
Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
"All of this is for nothing if we don't go to the stars" - JMS/B5
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