Date: Tue, 25 Jan 2011 19:44:56 +0000 (UTC) From: John Baldwin <jhb@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-7@freebsd.org Subject: svn commit: r217836 - stable/7/sys/vm Message-ID: <201101251944.p0PJiuC5048015@svn.freebsd.org>
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Author: jhb Date: Tue Jan 25 19:44:55 2011 New Revision: 217836 URL: http://svn.freebsd.org/changeset/base/217836 Log: MFC 214144: - 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(). Modified: stable/7/sys/vm/vm_map.c stable/7/sys/vm/vm_map.h Directory Properties: stable/7/sys/ (props changed) stable/7/sys/cddl/contrib/opensolaris/ (props changed) stable/7/sys/contrib/dev/acpica/ (props changed) stable/7/sys/contrib/pf/ (props changed) Modified: stable/7/sys/vm/vm_map.c ============================================================================== --- stable/7/sys/vm/vm_map.c Tue Jan 25 19:44:42 2011 (r217835) +++ stable/7/sys/vm/vm_map.c Tue Jan 25 19:44:55 2011 (r217836) @@ -336,15 +336,11 @@ 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: stable/7/sys/vm/vm_map.h ============================================================================== --- stable/7/sys/vm/vm_map.h Tue Jan 25 19:44:42 2011 (r217835) +++ stable/7/sys/vm/vm_map.h Tue Jan 25 19:44:55 2011 (r217836) @@ -246,7 +246,7 @@ 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 */ }; #ifdef _KERNEL
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