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- Make 'vm_refcnt' volatile so that compilers won't be tempted to treat

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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
This commit is contained in:
jhb 2010-10-21 17:29:32 +00:00
parent 24f2e3e959
commit 2d6ab8853a
2 changed files with 2 additions and 6 deletions
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6
sys/vm/vm_map.c
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@ -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);
}

2
sys/vm/vm_map.h
View File

@ -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