Date: Fri, 28 May 1999 03:07:11 +0400 From: Dmitrij Tejblum <dima@tejblum.dnttm.rssi.ru> To: Doug Rabson <dfr@nlsystems.com> Cc: Hidetoshi Shimokawa <simokawa@sat.t.u-tokyo.ac.jp>, alpha@FreeBSD.ORG Subject: Re: Panic: warning: pmap_changebit didn't. Message-ID: <199905272307.DAA01718@tejblum.dnttm.rssi.ru> In-Reply-To: Your message of "Tue, 18 May 1999 21:19:00 BST." <Pine.BSF.4.05.9905182107570.509-100000@herring.nlsystems.com>
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Doug Rabson wrote:
> On Wed, 19 May 1999, Hidetoshi Shimokawa wrote:
>
> > (gdb) print pa
> > $1 = 350412800
> > (gdb) print *pte
> > $2 = 183717226090783
> > (gdb) print faultoff
> > $3 = 10
> > (gdb) print /x pa
> > $4 = 0x14e2e000
> > (gdb) print /x *pte
> > $5 = 0xa7170000111f
> > (gdb) print /x faultoff
> > $6 = 0xa
> > (gdb)
>
> This is very odd. The page isn't marked as PG_MANAGED somehow but that
> doesn't make sense. The page is in user space but doesn't have any user
> read/write permissions.
Actually, it seems the page is in the upages, since the fault is in
|#5 0xfffffc000046a1dc in swapout (p=0xfffffe000cdf9340)
| at ../../vm/vm_glue.c:510
on this line:
++p->p_stats->p_ru.ru_nswap;
So, it's ok that the page isn't marked PG_MANAGED and don't have any
user read/write permission, but it isn't ok that it is marked
PG_FOR | PG_FOW | PG_FOE.
It may happen if something accessed upages of a swapped out process.
In this case vm_fault will pmap_enter a zero page in place of the upages.
That may explain this panic and 'pv_table is inconsistent' panic.
Recently a couple of potential invalid access to upages were fixed: the
ones related to calcru() and in alpha/alpha/mem.c. Frankly, I thought
that fixed the panic. But today I implemented reliable detection of
invalid access to upages, and found another one.
In trap(ALPHA_IF_CODE_FEN), and probably in other places, fpcurproc may be
swapped out.
I see following solutions:
- move pcb out of upages
- keep fpcurproc locked in memory: when we change fpcurproc, PRELE
old and PHOLD new.
- fault fpcurproc in when the FPU state need to be saved
- disable swapping forever
Dima
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