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Date: Thu, 07 Mar 2002 19:25:01 -0800 (PST)
From: randy@rcreighton.org
To: freebsd-stable@freebsd.org
Subject: RE: patch (was Re: reproducable panic with python)
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Sorry for seeming like a dunderhead, but I have a 486 that will compile a
kernel without problems but crashes with a page fault under heavy load while
running as a natd gateway. I chalked it up to intermittant hardware, will this
patch possibly fix my problem?
 
thanks,

Randy
On 07-Mar-2002 Matthew Dillon wrote:
>     This should fix it.  Included below is the test program to reproduce
>     the panic and the patch that will fix it. 
> 
>     The mmap() that triggers it is a MAP_ANON|MAP_NOSYNC mmap.
> 
>     I am starting a commit cycle now.  
> 
>                                               -Matt
> 
>#include <sys/types.h>
>#include <sys/mman.h>
>#include <stdio.h>
>#include <fcntl.h>
>#include <unistd.h>
>#include <assert.h>
> 
>#define SIZE    (512*1024*1024)
>#define SYNC    (1*1024*1024)
> 
> int
> main(int ac, char **av)
> {
>     void *ptr;
> 
>     ptr = mmap(NULL, 4096, PROT_READ, MAP_ANON, -1, 0);
>     assert(ptr != MAP_FAILED);
>     ptr = mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_ANON|MAP_NOSYNC, -1, 0);
>     assert(ptr != MAP_FAILED);
>     msync(ptr, 4096, 0);
> }
> 
> 
> Index: vm/vm_map.c
> ===================================================================
> RCS file: /home/ncvs/src/sys/vm/vm_map.c,v
> retrieving revision 1.187.2.12
> diff -u -r1.187.2.12 vm_map.c
> --- vm/vm_map.c       10 Nov 2001 22:27:09 -0000      1.187.2.12
> +++ vm/vm_map.c       7 Mar 2002 03:45:42 -0000
> @@ -1741,8 +1741,11 @@
>                * to write out.
>                * We invalidate (remove) all pages from the address space
>                * anyway, for semantic correctness.
> +              *
> +              * note: certain anonymous maps, such as MAP_NOSYNC maps,
> +              * may start out with a NULL object.
>                */
> -             while (object->backing_object) {
> +             while (object && object->backing_object) {
>                       object = object->backing_object;
>                       offset += object->backing_object_offset;
>                       if (object->size < OFF_TO_IDX( offset + size))
> 
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E-Mail: randy@rcreighton.org
Date: 07-Mar-2002
Time: 19:19:38

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