Date: Thu, 21 Oct 2010 17:29:33 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r214144 - head/sys/vm Message-ID: <201010211729.o9LHTXEv098032@svn.freebsd.org>
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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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