Date: Wed, 6 Mar 2002 19:51:39 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Mike Tancsa <mike@sentex.net>, David Malone <dwmalone@maths.tcd.ie>, Harry Newton <harry_newton@telinco.co.uk> Cc: freebsd-stable@FreeBSD.ORG Subject: patch (was Re: reproducable panic with python) Message-ID: <200203070351.g273pdb63445@apollo.backplane.com> References: <867koq7gp7.fsf@basilisk.locus> <20020306220959.GA47881@walton.maths.tcd.ie> <5.1.0.14.0.20020306205947.0513fcc8@192.168.0.12> <5.1.0.14.0.20020306222755.04151720@192.168.0.12>
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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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