Author: jhb
Date: Thu Oct 21 17:29:32 2010
New Revision: 214144
URL: http://svn.freebsd.org/changeset/base/214144
Log:
- Make 'vm_refcnt' volatile so that compilers won't be tempted to treat
its value as a loop invariant. Currently this is a no-op because
'atomic_cmpset_int()' clobbers all memory on current architectures.
- Use atomic_fetchadd_int() instead of an atomic_cmpset_int() loop to drop
a reference in vmspace_free().
Reviewed by: alc
MFC after: 1 month
Modified:
head/sys/vm/vm_map.c
head/sys/vm/vm_map.h
Modified: head/sys/vm/vm_map.c
==============================================================================
--- head/sys/vm/vm_map.c Thu Oct 21 17:29:18 2010 (r214143)
+++ head/sys/vm/vm_map.c Thu Oct 21 17:29:32 2010 (r214144)
@@ -339,15 +339,11 @@ vmspace_dofree(struct vmspace *vm)
void
vmspace_free(struct vmspace *vm)
{
- int refcnt;
if (vm->vm_refcnt == 0)
panic("vmspace_free: attempt to free already freed vmspace");
- do
- refcnt = vm->vm_refcnt;
- while (!atomic_cmpset_int(&vm->vm_refcnt, refcnt, refcnt - 1));
- if (refcnt == 1)
+ if (atomic_fetchadd_int(&vm->vm_refcnt, -1) == 1)
vmspace_dofree(vm);
}
Modified: head/sys/vm/vm_map.h
==============================================================================
--- head/sys/vm/vm_map.h Thu Oct 21 17:29:18 2010 (r214143)
+++ head/sys/vm/vm_map.h Thu Oct 21 17:29:32 2010 (r214144)
@@ -236,7 +236,7 @@ struct vmspace {
caddr_t vm_taddr; /* (c) user virtual address of text */
caddr_t vm_daddr; /* (c) user virtual address of data */
caddr_t vm_maxsaddr; /* user VA at max stack growth */
- int vm_refcnt; /* number of references */
+ volatile int vm_refcnt; /* number of references */
/*
* Keep the PMAP last, so that CPU-specific variations of that
* structure on a single architecture don't result in offset
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