From owner-freebsd-stable  Wed Mar  6 20: 9: 1 2002
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Date: Wed, 06 Mar 2002 23:09:01 -0500
To: Matthew Dillon <dillon@apollo.backplane.com>
From: Mike Tancsa <mike@sentex.net>
Subject: Re: patch (was Re: reproducable panic with python)
Cc: freebsd-stable@FreeBSD.ORG
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Thanks very much Matt!  That did the trick!

         ---Mike

At 07:51 PM 3/6/2002 -0800, 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))

--------------------------------------------------------------------
Mike Tancsa,                          	          tel +1 519 651 3400
Sentex Communications,     			  mike@sentex.net
Providing Internet since 1994                    www.sentex.net
Cambridge, Ontario Canada			  www.sentex.net/mike


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